One more caveat. Make sure you're always aware of the things behind the item you're heating, if you decide to go that route. For example, if there's a piece of sheet metal behind the bolt, its going to get hot too. If the surface is painted, the paint could burn off. And what's mounted on the other side of that sheet metal? If its plastic, it will melt. If its fiber, it could catch fire. If its a fuel line, you're going to have a lot more problems than stuck bolts.
Be careful. You'll be literally "playing with fire".