I decided some time ago that I don't really care about morality,because my revealed preferences say I care a lot more about personal comfort than saving lives and I'm unwilling to change that. I don't think I'd be willing to spend £50 to save the life of an anonymous stranger that I'd never meet, if I found out about a charity that efficient, so for the purposes of a thought experiment I should also be willing to kill Frank for such a small amount of money, assuming social and legal consequences are kept out of the way by Omega, and the utility of possibly befriending Frank isn't taken into account.

That aside, though, I think taking the nanofab is actually the morally right choice. Two lives spent in an uncomfortable featureless room are worth significantly less than one life spent as a nigh-omnipotent god. I'm not sure if letting/making Frank continue to live in the uncomfortable featureless room is even of positive utility to him. If I knew there wasn't any more to life than the featureless uncomfortable room, I would be contemplating suicide fairly quickly.