First, I would storyboard it out, so you know exactly what you need to do.
But it sounds like you’ll need to rig up a pretty complex solution for this… which will include a few groups (for the pivot points of the box) and point/orient constraints. Somethin ya might want to think about, is (since you’re using IK) tryin constraining the hands to the box…well… they won’t be constrained to the box itself, but to objects that will be within the box’s hierarchy. You can then move these objects around the box and the wrists will stay constrained appropriately if you move/tilt the box.
I hope I’m not just confusing you… but I really can’t say much more without details. I once had to make a character build an object in his hands, while swapping the objects between hands. There’s tons of different ways to do it, but all of them will require a ton of planning.
Hmm… now that I think about it… Maya 5 has those new parent constraints that will probably help out a TON. So you might be able to get away with just using multiple groups and parent constraints. :shrug:
There’s a reason you don’t see much character interaction in demo reels. Good luck.