Adding something behind the panel sounds like the way to go to me.

I wouldn't, however, use hot glue to glue a nut to the back as it's guaranteed to break loose later (especially when it gets cold). Using it in the hole may be ok as it's not going to be required to stay stuck to anything.

I put in those green expanding thingies designed to screw into drywall in. They've held up for a few years now.