I've been experimenting with clothifying the collars and trying to simulate gravity effects, but had little success. Poser simulation does not support a volume constraint in the simulation and because you can only simulate one body part at the time you get 'hard' edges.

Tried breast bones also, but the movement is one of sliding parallel to the ribs rather than a rotation. I am not sure if weight mapping will do the trick. Maybe if it allows non-consecutive bones so you can simulate the sliding motion by a two-link rotation.

I am afraid we will have to wait a while before there is a satisfactory general solution.