The cheapest solution will be a left handed drill bit of the appropriate size, this will bite into the screw head and turn it counter clockwise. Next would be a set of easy outs, a.k.a. extractors. Next would be drilling the screw out, re-tapping one size up, and using a new screw. You can use a little heat to help loosen things, but don't go too crazy, there is a seal on the backside of the drive that keeps dirt and water out. You don't want to destroy that. You can also hold a large screwdriver by the tip, and hit the screw with the handle sharply a few times to help break it loose, if you don't have a plastic faced hammer. Undo the speedo side of the cable and remove the front wheel and get it up on a workbench or table, it will be MUCH easier to do. I had the same issue, and the drill worked for me. I used an allen screw and countersunk washer to replace it, as i hate the phillips screws Honda used. They used these damn screws so the farm boys on the line wouldn't over-torque the fasteners, according to Honda lore.