I have never tried it but on an episode of "trucks" they showed using a razor blades to gently scrape the top off of a run. The theory was that when trying to sand out the runs, you actually sanded thinner areas that naturally formed right around the run from the natural pulling of the paint as the run followed gravity. By scrapping with the blade, they only removed the high area of the run itself. Take it for what it's worth but it made sense to me.
