Well, since my reason for doing it is frivolous, I don't want to do anything drastic. I think the only way to get them out would be with a teeny-weeny drill.

I asked at the closest Mac emporium and they said it would probably be at least a 1 hour service charge minimum, including digging through the old screw pile to find some unstripped ones to replace the unfriendly ones. It's not the threads, it's the socket where the Torx grabs it that's become smooth and round instead of angled and edgy.