I put a metal window screen on top of an empty super and brushed the sugar through it onto the bees below. The bees sounded kind of pissed.
Three hours after dusting, there were 26 mites that had fallen off the bees through the screened bottom board. I was hoping for more, but mites are not a huge problem for my bees at this point. As long as I do this every three weeks or so, along with the removal of the capped drone brood (mites reproduce in drone comb), I hope to minimize the mite threat.
What could be better than bees coated with powdered sugar?