Some years ago I had a set of rubber/alloy brake dust covers. Basically they were cut to size and fitted over the brakes/wheel studs.
When the wheel was fitted they formed a barrier against brake dust getting onto the rim. The only downside was that the brakes could overheat, but only if you were giving a bit of wellie, in normal driving they were excellent. The alloy went over the studs and the black rubber surround covered all of the inside of the rim.
Does anyone know if they are still available?
Ps: Ah, just found these, but can you get them in England?
Kleen Wheels Brake Dust Shields - Lowest Prices Guaranteed