I would import them on their own and then parent them to the character when needed. Sort of like a weapon to hand. Of course these cloths need to be specifically modeled for that one body type.
I used to do it a little different a while ago. You can create vertex groups and parent them. Just like you do with bones. So I would model different torso. And parent the vertex group of the head to each different torso. Each vertex group for the heads and torsos need to be the same size,scale,and vertex amount. And of course you can do this for legs,hands,feet.