I'm trying to change out stock handle bars on my dahon D7. The GripShift handle appears to need be unloosened with a set screw. Needs a 2.5 size hex driver. I'm traveling and away from decent tools so I bought foldout set of Husky hex wrenched and I've tried to twist it and the walls of the set screw socket head are not holding up. I've had decent luck on mildly worn socket heads using a high quality hex driver but I don't have access to one. Any ideas how I can extract this screw?

- maybe use the flame from a cigarette lighter to heat the screw and hopefully not melt the plastic?
- drill it out?