Have you tried Poser's magnets? I don't mean to imply you don't know anything about Poser (and I'm not a modeler), but I've seen others that do mention magnets when making a morph for bending body parts. Of course, there are quite a few modelers here who are very knowledgeable in that area who will give you some help and great tips. But my first thought were magnets.

Laurie