The palm can be bent, either through a morph or (I think) via JCM or whatever they call it now. It's a matter of linking through the wrist to the first finger joint somehow. However, the problem being that you can only move it very small increments as the top of the hand tends to warp too. A carefull and clever morph target would probably be the best but I have tried and failed dismally to make anything that works even remotely well. To be honest I'm rather surprised that nobody has done one yet, though I guess most people just don't get that close to their model's hands to worry about such a small thing. :)