Don't rest him at all, if he's able to play.
I'm not saying they should do something crazy, like play him 20 minutes or so, but if Shaq can play on Sunday, I say they give him a few minutes or so, 5 or 6 if possible.
Because, at the end of the day, if Shaq is supposedly close to a return as early as Sunday, and can manage a good 5 or 6 minutes, or at least a good 3 to 4 minutes, why not do that? Because, at the end of the day, don't you think it's a good idea he gets some on court time in a real game before a possible series against the Heat? I can't say if it's entirely the right thing to do, to not play Shaq until a potential Heat series.
I'm not saying Shaq couldn't perform perfectly well enough, or at full capability in any series going forward without getting some time in against the Knicks, but I think it can't hurt to do it, if he's able to.