Not sure if you found a solution to your mirror issue, but similar to what another member had described, here's what I found on e-how:
1 Use the blow dryer or heat gun to warm the mirror mount right where it attaches to the windshield. You are applying this heat to soften the adhesive underneath.
2 Test the mirror every so often while you are heating it by trying to gently move the mirror slightly back and forth. Once you feel movement, continue to apply heat and increase the force a little at a time. Work the mirror back and forth and it will release from the windshield, leaving a fair amount of adhesive behind.
3 Warm the adhesive left on the windshield again. For thick patches of adhesive, wrap the fishing line around your fingers as if you were getting ready to use dental floss and press your fingers up tight against the windshield on either side of the remaining adhesive. Work the line under the top edge, and move the line back and forth with downward pressure. The line will cut through the adhesive and remove all but a little residue.
4 Apply the adhesive remover to the residue and use the razor scraper to gently scrape off the rest of the adhesive. Wipe the area with a rag and more adhesive remover.
5 Clean the area with glass cleaner.