creating scratches around edges

I’v moddeled a blaster of a battledroid of Star Wars. I now want to create realistic scratches around the edges and corners. I had the Idea, to paint the edged white in texturepaint mode. Then to use this mask in Gimp to paint with a scratchbrush on the edges.
But ich cant imagine, that it every time takes that long. Ist there a faster/better method to create a wite line one marked edges?
Some other ideas to make scratches on the edges?

Thanks for your help!

if you use the cycles you can render a map using the pointiness feature