I also use Griot's garage wheel cleaner, I have found that you have to provide some type of agitation no matter what type of cleaner you use. Often times soap and water will do the job with some good old fashioned elbow grease. My new wheels are gunmetallic finish to combat this issue! Good luck.
2013 M5 delivered 8/25/12: AW, SO, Exec Package, ADV10 DC from WB
2012 Challenger SRT8: B/B, custom CAI, Borla Catback exhaust, Vossen VVSCV3, 8lb Magnusson Supercharger 670HP
2012 VW Golf R daily driven Stage II+ APR tune, 360HP