At the end I just noticed, that he best solution here would be creating dynamic clothing figure not prop.

If you convert your prop to figure all mesh should be one body part. I think abdomen. This part of cloth. Belt should be choreographed group instead constrained, rest should be dynamic.

Best bone donnor is figure which you use. If there is too many morphs, delete all bones except abdomen, hip and chest. They are neccesery to bend choreographed group.