How about using a heat gun (NOT a Hair Drier) followed by dry ice? I saw a video a while back where the guy put some aluminum foil foil over the dent & lightly passed a propane torch over the dent followed with dry ice and it popped the dent out. Unfortunately I can't locate that video now.
When doing body work when I was going to do a complete repaint I've used a torch to heat the panel followed by a rag soaked in cold water and that popped the dent right out. Again I was doing a lot of body work and a total repaint so I wasn't worried about saving my paint.
Here's a link
https://www.youtube.com/watch?v=y9OGa9vB42Q
Here's one using boiling water
https://www.youtube.com/watch?v=J79uO_H0kzo
Boiling water followed by dry ice might work out well in your case.