how about painting on something like release paper? The paint would not even touch the vehicle surface, and it would be easy to remove...could even be removed carefully and saved if someone wanted to.
clean the surface and carefully apply the release paper so there are no ripples or bubbles, and any seams match up exactly, or maybe slightly overlap. Paint whatever you are doing, then carefully cut around it and remove the excess paper. Any excess glue left from the paper, if any, would be much easier to remove then any kind of paint.
Of course, by cutting the paper that means you always have a hard line, so if you want the softer edges that an airbrush is known for, then you would need to paint a base color background that you could cut through, and have the softer edge inside of that.
Last edited by Yota Bill; June 11th, 2011 at 10:32 AM.