Originally posted by cgoudie I'd probably try a Home Depot to see if they have a screw remover bit small enough for you. That would be my first choice.
I've never see this lens, so take this next bit with great caution.
You could, (and I stress could) ever so carefully use a very small drill bit to remove the head of that screw. If you do that It might be possible to grab the remains of the screw (once dismantled) with some fine needle nose pliers and remove it.
This sounds like an extremely risky proposition to me. I would probably try a shop first, and then if that's too much mula, I'd swing for the fences.
I agree, the screw is probably countersunk so the head will be flush with the surface. Removing the head by carefully drilling it off will enable you to remove the 'part' and leave a bit of the screw thread exposed, which you can grip with pliers or maybe vice grips.