This will alleviate the problem, but will not solve it completely, as a small amount of dust will always remain in the system, and will come back into the alu-fins of the heatsink. Also, make absolutely sure that you block the fan from spinning as you're blowing air into the fins, especially so when using high-speed/highly pressurized air. You wouldn't want to damage the fan's bearings and/or force the oil out of it (if it's a sleeve/rifle/hysint/hydrodynamic bearing). You could use an unbent paperclip or something similar to push through the ventilation openings under the fan to stop it from moving. It may, but only if it's flow is focused tightly enough, with a nozzle or something. Otherwise, it simply won't have enough dynamic pressure to be effective.