Well, I push on the tip side of the screw with a gig needle while turning the screw head with the screwdriver, its a bit tricky as your hands get tangled a bit but if you've ever removed a double screw case pin then you should be used to that move.... :lol:
If not try to brace the case between your knees while pushing with the needle on one side and turning the screw head on the other, dont be afraid to push really hard with the needle, makes all the difference in the world...