If you put a spacer in, you are just going to have less room to the fender. He pulls 10mm for more clearance for the wheel.

I never say you cannot do it, but with what he wants to do (no negative camber), he just cannot, Specially if he has coilovers already (which mean less room).

Widebody your car, Modify the rear quarter panel, and you would be able to do it.

My last question is what kind of mods you have on your car.