Here's an install on a non-M Z4 coupe. I believe we could essentially do the same thing, but we have a different front suspension setup. Ours is closer to an E36 configuration than E46, but I'm not sure if E36 backing plates would work without some modification. I think you could modify the stock backing plate by cutting a hole and riveting on a duct,
similar to this. I would either try to modify the backing plate in place or cut it off so I wouldn't have to remove the wheel bearing (unless I needed to replace the wheel bearing.) It would also make sense to run the intakes to the center grill and modify it so the outer holes are actually open
as seen here.