I haven't tried it but I found two threads in the search engine that mention tapping it off with a piece of wood, both mentioned it is held on with pot metal studs that are flattened from the inside where you can't get to them.
Pop up Gas Cap Emblem removal on a 67(pics included)
The only other way I can see is to drill out the center 'cap' piece on the inside of the cap to get access to the screw and spring.
"If it ain't broke, I haven't fixed it yet"
1967 Coupe 333ci CandyApple Red w/red int., AOD, 9" 3.50:1, Front PDB
'09 Warriors In Pink V6 w/glass roof - wife's Stang