You mean the adaptors to lock the wheels? I thought BMW sold those. I know you can add Thule/Yakima racks on to a BMW, but never heard of someone stacking an aftermarket rack on top of the factory one. People say the aftermarket rack is nicer cuz they can come with a fairing in the front that reduces wind noise. But, the factory one mounts in those special mounting points so it looks flush with the car.