That blue stuff has given me problems in the house too.
I have heard of covering the line with clear. I have also heard of using an extremely fine sandpaper for evening out the line. Sanding to me though sounds dangerous (but I have no experience here).
Check out the Autobodystore.com forums.
I have never done any work like this but it seems the problem you describe is the same one you would encounter doing stripes or flames. there are several discussions on this at the Autobodystore.
