I just use an old microfiber wash mitt. Used to use it on the car itself, but now that it's older I just use it on the wheels (don't use it on the car again). Gets in there good enough, but the best way to clean the wheels 100% is to take them off, and yes it's a huge pain.
Although, the EZ Detail wheel brush does a pretty damn good job.
'11 BMW E92 ///M3 - ZCP and DCT
'15 Ford F-250 - Lariat, 6.7 Powerstroke Turbo-diesel