Sometimes a sharp screwdriver or a sharp blade can help. A cheap screwdriver can be easily sharpened and made smaller when needed so it might just help to do the trick in turning the screw.
Or take a cheap (small) drill 1mm or so, break the top of with pliers so you get a sharp tip and try using this to get a grip on the screw.
Make sure the drill turns very slow and the right way around. Lefty loose, righty tighty