So, on your use of 'end', an 'end' cannot be objective and unconditional? I think that's a highly uncommon use of the term.

No, I just should have been clearer that when I said "stated end" I meant "subjective, desired end". As commonly used, 'end' includes unconditional ends, I just haven't ever been presented with an argument that persuaded me to think that such ends exist.

one important constraint on any interpretation of any 'ought to X' is that it should be positive towards X as opposed to negative or neutral, in favor of some action or attitude as opposed to against it or indifferent. But a mere predictive causal claim doesn't have any valence at all: it's just a neutral claim about what will probably lead to what, without anything positive or negative. So any attempt to reduce oughts to predictive causal claims seems doomed to failure.

Sure, you can stick that feature into your meaning of 'ought' if you want. But I'm not going too deep into the conceptual analysis game with you. If you want to include positive valence in the meaning of a hypothetical ought, then we could translate like this:

"If you want to stretch, you ought to stand" -> "standing will make it more likely that you fulfill your desire to stretch, and I have positive affect toward you standing so as to fulfill your desire to stretch"

As I said in my post, expressivism is fine - and certainly true of how many speakers use normative language. I happen to be particularly interested in those who use normative language cognitively, and whether their stated moral judgments are true or false, and under which conditions - which is why I'm investigating translations/reductions of normative language into natural statements that have truth conditions.