I just experimented a little and found that a simple brush (unused, preferably) or an eraser-pen (like this:
http://www.jako-o.de/mb3_media/1/560/d/0/2/671197_1.jpg or like this:
http://4.bp.blogspot.com/_nqngWsqaJP...0/CIMG0098.JPG - or the eraser-side of a pencil) work as well
