Why in the hell would you install a router inside your PC, i cannot fathom why anyone would need to, short of being extremely tight for space.
You could always have the modem/router in another room/cupboard, then use powerline adapters to carry the ethernet connection.
I'd suggest asking your client what problem he is trying to solve by having the router inside the PC, i cannot imagine having the router in the PC it is the best solution available to him.