Heat it up with a blow torch around the outside of the head tube (until red hot), then dunk it in cold water and use your tool, will DEFINITELY work after a few heats and dunks, BUT it will damage the paint, so depends how desperate you are to get it out. I have used this on car bearings, alot bigger and a lot stucker (??). I once had a awkward headset in a bmx frame, broke one of them headset tools trying to get it out (snapped a tooth) and didnt have a blow torch at the time, so i put the headset cup into a vice, tightened it right up and twisted the frame, it came loose after a few twists and then came out with the broken headset tool! (Maybe give that a go, might scratch to headset though!)