1. I'd get a #2 phillips hexagonal bit for one of those screwdrivers that take replacable bits.
  2. I'd grind the sucker down from the but end far enough so it'd get into the space and insert into the screw head with enough clearance for the screw to back out. 3/8 inch should be enough.
  3. I'd get an end wrench sized correctly for the hex of the bit. Holding the bit into the screw with a flat blade screwdriver of some such tool, I'd turn her out with the end wrench.
  4. After getting it all apart, I'd notice what the trick was and feel real stupid.