Short of washing every few days, or swapping out your pads, there's not a heck of a lot you can do, unfortunately. I've heard of guys using dust shields, but doubt the effectiveness of them.
The dust is a symptom of the pad material shredding off as it comes into contact with the rotor. Some brake pads are worse than others — you should see how black Porsche wheels get after 20 minutes at the track. Metallic brake pads are the worst. Ceramic brake pads are the best as they have fewer metal particles, but may cause squeal, which is worse than the dust in my opinion.
Think of the dust as evidence your brakes are hard at work. Gentler stops will help too.