Now that the socket is clear of glass mix up a chunk of the epoxy putty and carefully pack it into the bulb stump.
Be sure that the epoxy does not touch the surrounding socket or you will glue the stump in!
While the epoxy is still soft stick your screwdriver into the epoxy making an oblong cavity. wait for your epoxy to fully harden. now using that cavity simply use the screwdriver to unscrew the bulb stump.
TaDa! the stump is free.
I came across this technique when the bulb in my refrigerator went out and the entire intact glass came out of the socket leaving the threads slightly rusted in place and in a position I could not reach. I had to use a mirror to even see the socket and after multiple failed attempts and 4 months it occurred to me to buy some epoxy putty.