How can I creat a moduler character model with soft skin weights?

I am trying to create a modular character with different parts that can be swapped out. I need the look to be seamless so I have vertices on one model that line up perfectly with vertices on another (for instance the ring around the wrist on the hand and the arm lines up). The problem I'm having is that I also need smooth skin weights on these modules. Keeping with the example, the wring of vertices around the wrist need to be partially skinned to the hand and the arm, but each vert is really 2 verts on 2 separate models. How can I create one game object with multiple swappable parts that are all skinned to the same skeleton?