Check this stuff out, it might work quite well for what you want.
http://www3.towerhobbies.com/cgi-bin...&I=LXC099&P=ML
It is called liquid mask. It is basically a white paint that you put on with a brush. When it dries, it turns clear and has a rubbery almost silicone like feel to it. You can draw on it with a pen, then you just use and X-acto nife to cut out the line, then peel away what ever you want to paint. RC guys use it to paint all kinds of intricate little flames and designs on the RC cars. You have to be able to cut a straight line though. There are different size bottles if you search on the website if you think it will take more.