The eraser is a great tool. I've always used my heat gun AMD a razor blade for stuff like that, but you gotta be good with a blade. I get up real tight to the heat gun and keep the blade's sharpened edge angle the same as the surface you are on, and push slowly into the hot glue.
It can burn your fingers of you hold the metal blade with heat blowing on it, I usually wear gloves.
Im not guaranteeing you wont scratch it, but ive become pretty damn good at it, most of the time there isn't much glue left at all either. But of course every vehicle is different, and the older and more weathered it is, the more of a pain in the face it'll be