I had a similar problem with my Motorola Renew phone but was able to solve it without disassembling it. I slipped a pocket knife blade behind the screen on the top right corner and pried it open a little bit (2-3 mm), then set my air compressor output pressure to 90 PSI and sprayed out the dust with a high powered blast. I think you were on the right track with the spray can, but perhaps needed more air pressure to get the particles out. If you don't have access to a compressor (I have a simple 6 gallon pancake model from Sears), maybe you could stop by a local gas station or car repair shop (anywhere that mechanics use a lot of air tools) and see if they could help out.