The OEM BMW brake pads are notorious for excessive brake dust. In many cases you can simply replace the OEM pads with aftermarket pads (like akebono ceramic pads). This is what I did with my prior 7-series and the difference was like night & day. Here is the mfg website. You can use it to look up your part number for your vehicle and then you could contact one of the forum sponsors to see how much they would be. Of course any such part would not be covered by BMW's service or maintenance policies since those specify "original BMW parts ONLY" and you should be aware that ceramic pads WILL wear your rotors down quicker and that consequently BMW maintenance may also not pay for replacement of those within the warranty period.
http://www.showmetheparts.com/akebono/