I would PUT IN WRITING that you are only agreeing to do that barebones work, that you are doing it from home, and then I would LEAVE the computer, whether to laze about or wander the streets for a bit.

That way you are not leaving them in the lurch, but again, no non-profit-vampirism shit. Remember that you are leaving because they treated you badly, and you are no longer responsible for what occurs there.