True. However, if you already can source for a precision engineering shop in the area to do it for you its quite a bolt on install to the car once they are able to modify the rear discs. For my case, the shop charged me ~USD77 for this mod. I would have much prefer going with all matched parts like the bigger eBrake, springs, clips etc from the 330i being fitted. So for my case its just a workaround.
Here are pics of the inner drum of the modified discs with the spacer installed.
Here's how they secured the spacer. They bolted it down to the drum and then repainted the drum after. This pic was taken before the repaint and shows the position of the bolt which was inserted.
