I did post this on another thread, so hope it's ok to repeat it here as it may help.
For what it's worth, and please don't laugh, but when I had my 330Ci Sport the best thing for cleaning the wheels was a pair of rubber gloves I don't know what it is about BMW brake dust, because it didn't work so well on my Boxster, but using my Marigold clad fingers to wipe the wheels used to work a treat at removing the muck, followed by a rinse with the hose. I have to say I have quite small hands so I could fit my fingers in the nooks and crannies, but it used to work every time!
As a girlie I am not averse to wearing pink rubber gloves, but perhaps for some of you geezers the ordinary clear latex gloves might work just as well?