The problem with steelmanning YEC is that you can't do so without converting it into something that YECists would vehemently disagree with. For example, you could state that God created the world via an evolutionary algorithm, then implemented it recently, and either the Flood was a small local event or the layer in question was deleted from the record. This however would seem more like entirely rejecting YEC. You could say that God made it seem like evolution was true as a test of faith, but such is a universal explanation that has no predictive power, plus the bit about calling God a liar.
You could also reject the data -- claim that there is a massive conspiracy among all scientists to pretend that the fossil record looks like millions of years of evolution, migration, extinction, etc., instead of looking like ~2000 years of land and marine life covered with a year of massive flood sediment covered by ~4000 years of land and marine life, and also a conspiracy in the genetics community to cover up the fact that there was a genetic bottleneck of all species down to one or seven pairs of animals ~4000 years ago, and also that the rate of evolution is actually millions of times faster than scientists say it is, and a few others like that. Notable creationists like Ken Ham are obviously ringleaders of the conspiracy, else they would be decrying the conspiracy instead of acknowledging that data and pretending that a flood is really good at sorting by species things like pollen.
Some things are just really hard to steelman. The most convincing arguments for YEC, and most pleasing to its adherents, are those that argue as though science was about explanations, rather than predictions.
Note: for much of my life, I believed (gave roughly equal credence to vs evolution) in YEC. I maintained this via privilaging the hypothesis, motivated skepticism and related reading from AIG, until one day I made the "mistake" of saying I would change my mind if someone would provide , which someone did. Contrary to Bill Nye's fears that this belief would somehow cripple me in science or technology, it was compartmentalized into irrelevance, and in fact I was usually considered one of the smart kids in class. In fact, it was because of people from Ken Ham's group that I had in the same compartment as YEC not science, but religious belief (and therefore also many moral and political beliefs). As such, the fact that I'd have to restructure my core beliefs made me hold on to YEC for a couple more years. However, I think others don't take their beliefs as seriously as I do. Ken Ham, for example, doesn't actually believe YEC because it does not constrain his expectations (nothing would change his mind, as he has admitted).
In a recent discussion of steelmanning, I observed that few people around here seem interested in steelmanning young earth creationism. In the resulting subthread, someone suggested Yvain's steelman of the Time Cube as illustrating what a steelman of of young earth creationism might look like. But steelmanning the Time Cube may be too much of a stretch, it's a little too incoherent to steelman effectively without changing it into something else entirely. In contrast, once I thought about it it wasn't hard to come up with some ways to steelman young earth creationism in a way that was very much in keeping with the spirit of real young earth creationist writings.
The way to do it, I think, is to approach it from a philosophy of science angle. For example, here's a quote from an article titled "Creation: 'Where's the Proof?'" on Answers in Genesis, a website run by young earth creationist Ken Ham (who recently debated science guy Bill Nye):
You find a lot of this kind of thing on Answers in Genesis. For example, they're willing to concede that on certain assumptions, radiometric dating is a strong argument that the earth is a lot more than 10,000 years old, but they deny that they need to accept those assumptions.
I honestly don't think it's much of a stretch to steelman this into something that would look a lot like some of the things the philosophers of science I studied in graduate school said. I started writing a long post spelling this out, but then I started worrying I was going too far in playing devil's advocacy for creationism (even for an exercise in exploring the weaknesses of steelmanning). So instead, I'll just mention some places too look for material in such a project: The Duhem-Quine thesis, confirmation holism, underdetermination of scientific theory. Fun fact: Pierre Duhem regarded the existence of atoms as a metaphysical question that could not be settled by experiment, and this has not stopped him from being regarded as an important contributor to philosophy of science. I suppose Feyerabend belongs on the list too, but that's almost too easy (even though, yes, I did have to study Feyerabend in grad school).
Oh, and I could even find material for my steelmanning of young earth creationism in the writings of Robert Pennock, a philosopher of science who testified against Intelligent Design at the Dover trial. Some philosophers, while thinking creationism is dead wrong, have criticized the reasoning used in that and other court decisions that have kept anti-evolutionism out of public schools in the US. Pennock wrote a response, titled "Can’t philosophers tell the difference between science and religion?" where he argued, among other things, that methodological naturalism (MN) is essential to science and supernatural claims are inherently untestable. A relevant quote:
So on Pennock's view, testing young-earth creationism and thereby demonstrating it to be false is not possible without relying on naturalistic assumptions. This creates an opening for the creationist to question whether science needs to rely on naturalistic assumptions, and argue that one could create an equally valid version of science based on (fundamentalist) Christian assumptions.
You might conclude Pennock is wrong about this, and young-earth creationism really has been straightforwardly refuted by science, but this creates a different opening for the creationist: argue that if Pennock is wrong, his ideas really shouldn't be the basis of court decisions about whether creationism can be taught in public schools. Evolutionists could respond by arguing for some other philosophical basis for rejecting creationism, but then they'd probably have to make some contentious philosophical claims and we shouldn't be determining what children can learn based on contentious philosophical claims either.
An argument along the above lines could also be used for a different purpose, by someone who rejected creationism but wanted to make a show of being fair-minded towards their opponents and generally more rational than most of their peers. The thing to do is to say that while young earth creationism can be decisively refuted, most scientists and philosophers botch the philosophy required to do that, and this indicates their rejection of creationism is mostly tribalistic, and the young-earth creationists don't actually come out looking so bad by comparison.
Speaking as Chris Hallquist and not some hypothetical alter-ego, I think that if a philosophy of science makes young earth creationism come out looking good, that's a reductio for that philosophy. I think educated people who reject young earth creationism are generally rational to do so, even if their philosophy isn't that hot. Still, I'd be curious to know what else people on LessWrong can come up with in the way of steelmanning young earth creationism.