Hi Dan
Did you solve this problem? I’m trying to work out something similar myself.
Have two characters, a mother and child, both rigged within precomps with DUIK. The mother picks up the child and I want her arm to be in front of him (the rest of her body all behind.) The only way I can see to do it is do the animation in the two separate precomps, duplicate the mother and put the duplicate version on top of the child, then mask out her arm and move the mask frame by frame.
Feels like a painful way to do it but I can’t work out another way!