Jet, to you consolation ))) You always have a choice: either modify the original piece for M Sport, or bit a bullet and make M5 conversion (great example is here:
http://f10.5post.com/forums/showthread.php?t=1038584) With the last one, whatever fits M5 front and rear, will finally fit the converted M Sport car, also including front wheels with crazy offsets of 10 or so). I have general understanding how people do the conversion, but it looks a bit too much for me) Love M Sport as is, and who's got the M5 is lucky having the exclusive thing.