I don't think that existence is subjective, so universal preference either exists or it doesn't. It has been a long time since I've sat in a philosophy class though, so I'd welcome a correction.
Whether a preference is universal is sufficiently impractical to ascertain with certainty (especially since you have said you want to include the preferences of people in the past), such that any belief about the existence of any universal preferences is inherently subjective.
I'm not talking about whimsical preference, I'm talking about group membership defining attributes - preferences that make one a human being and that every other human has or will share. And yes, this would define a human being even in a world were no human ever existed or will exist.
So... you are talking about preferences that 'define a human being', but then those preferences are only tautologically universal (since you are excluding any possible exception). This seems absurd.
So if I were to tell you that I really did prefer to be a slave you would say I am not human? You are excluding as 'human' any individual who are not capable of understanding the concept of 'ownership'. Do you seriously believe that babies and the severely mentally handicapped are not human?
If you are operating with such a divergent notion of 'human' (and thus 'morality', 'universal' and 'preference') then there is no point in having any further discussion with you or considering anything you have to say.
Nope, exceptions get their own subclass. Babies would be baby-humans, the mentally ill would be - well you get the idea. These classes are actually a predictable reality given an accurate definition of "human being", a component of the whole. Imagine a dependency graph, with the edge cases as leaf nodes. So the definition of human isn't related to a single entity, or the averaging of the qualities of the entire population - it is related to the attributes that give rise to the entire structure - seed values. Again, this has nothing to do with time, so "give rise to" is more like a logical conclusion than a sequence of events.
You should be aware that there's a significant risk you'll have to turn every single human who ever lived into its own class, and even then you'll run into the Halting problem while trying to identify each case of each classification.
You won't end up with any single seed values you can match any given instance against, but with multidimensional matrices that represents multidimensional scales.
