A few people have recommended the covers that fit inside your wheel to keep brake dust form reaching that area. There are two problems with these covers;
1. The brake dust still coats the inside of your wheel and since you can't see the dust without removing the wheels, this can lead to neglect which may ruin the paint on the inside of your alloys.
2. These covers reduce the amount of airflow to the brake caliper increasing heat which can lead to even more brake dust. Yes, the covers have vents, but they are small and really don't do much.
The best solution that I have found is to;
1. Purchase a brake pad that doesn't dust quite as much.
2. Remove your wheels every 3-4 weeks ad give them a thorough washing followed by paint work cleanser and a coat of polymer wax. The polymer waxes will hold up to the high heat generated by the brakes better than a natural carnauba based wax. A coat of wax will assist in keeping the brake dust from attaching to the paint surface.
3. Get a couple of microfiber towels and use these to wipe the dust off every 2-3 days.
Now for a few links;
Brake Pad Comparison
Hawk Brake Pads