Another approach might be to dump in a whole bunch of data, and hope that the simplest model that fits the data is a good model of human values (this is like Paul Christiano's hack to attempt to specify a whole brain emulation as part of an indirect normativity if we haven't achieved whole brain emulation capability yet: http://ordinaryideas.wordpress.com/2012/04/21/indirect-normativity-write-up/). There might be other sets of data that could be used in this way, ie. run a massive survey on philosophical problems, record a bunch of people's brains while they watch stories play out in television, dump in DNA and hope it encodes stuff that points to brain regions relevant to morality etc. (I don't trust this method though).