Doing a little light reading on the interwebs today about bumpstops and the E90 platform, most recommendation are to not cut the bumpstops when lowering the car as it changes the progressive combined spring rates, instead to use a shorter bumpstop from other BMWs, i.e. E36 M3 Front and E85 Z4 Rear. Since the sleeves seem to be the biggest difference between E9X and E84 it may also work for us. Here is one of the many threads:
http://www.e90post.com/forums/showthread.php?t=614778