This doesn't really work, because once you are in an acausal context, the notion of "precommitment" becomes quite redundant. The AIs' bargaining position in acausal trades is whatever it is, as is yours. Of course I have not studied the matter in detail, but one possibility is that a Coasean result obtains, where you make precisely the acausal trades that are efficient, and no others. Since, at the end of the day, Roko's basilisk is just not that plausible (overall, the risk of UFAI seems to come from garden-variety scenarios of things going wrong in ways we'd know little about), it makes sense to just work on building FAI that will pursue our values to the best of our ability.
Precommitment isn't meaningless here just because we're talking about acausal trade. What I described above doesn't require the AI to make its precommitment before you commit; rather, it requires the AI to make its precommitment before knowing what your commitment was. As long as it irreversibly is in the state "AI that will simulate and torture people who don't give in to blackmail" while your decision whether to give into blackmail is still inside a box that it has not yet opened, then that serves as a precommitment.
(If you are thinking "...
Todays xkcd
I guess there'll be a fair bit of traffic coming from people looking it up?