Hey Arran

Looks like a bit of a dilemma.

I'm not entirely sure how you would go about deforming the cloth with a rig?? Maybe pose him and then use a lattice to deform the cloth to match?

Or if you create a rig you might have to move it sepperatly from the body's rig (think this would get the best results to be honest).

The other option would be to use some sort of cloth simulation, maybe softbodies with a goal and springs to deform the clothing as the rig moves (if you make the softies collide with the body)?? If youve got 8.5 then using nCloth should be able to do this pretty well.

Hope its some help, sure youll get round it