Having my own detail shop- I have a trick that I have passed on for brake dust problems-especially on MB's. It does not require changing pads or dust shields.
Try using a household 'dusting' product- which is basically wax- (I use Endust -the one that helps repell dust after applied). Make sure to clean the wheels first, then dry, and apply a good amount of dusting product to a cloth or carefully spray onto the rim in a circular motion, then polish dry. You will notice that the rim will be very smooth, dry and slippery.
It also helps cut down on accumlative brake dust and makes the dust that sticks easier to get off. Its similar to waxing your wheels but much faster and easier to do on a weekly basis when you have a few minutes.