Ok,

I tried the heat gun in the head tube, plus some dental floss. I had a small heat gun from Radio Shack that fit nicely into the head tube. I don't know if I got it quite hot enough, I really had to work it with the dental floss to get it off. I broke several pieces of floss.

I do think the floss was slightly too thick, but I'm not quite sure what would be strong enough, and thinner. The glue layer was very thin, no heavy foam like apparently is used with some car badges.

It did finally come off, but with some minor distortion.