If your values are such that they do not even allow a mechanism for creating an best effort approximation of values in the case of ontological enlightenment then you are out of luck no matter what you do.

If preference is expressed in terms of what you should do, not what's true about the world, new observations never influence preference, so we can fix it at the start and never revise it (which is an important feature for constructing FAI, since you only ever have a hand in its initial construction).

(To whoever downvoted this without comment -- it's not as stupid an idea as it might sound; what's true about the world doesn't matter for preference, but it does matter for decision-making, as decisions are made depending on what's observed. By isolating preference from influence of observations, we fix it at the start, but since it determines what should be done depending on all possible observations, we are not ignoring reality.)