There's a few different things you could try. If you can get a piece of elastic, preferably an elastic band, you could put the elastic over the tip of the screw driver to fill in the space. Sometimes slightly tightening the screw first will break the seal between the plastic and the screw, making it easier to unscrew. You could also try a small hand drill from a modeling kit to make the screw bit a little deeper, so the screw driver can get a tighter fit. You could try hitting the screw driver with a hammer while its sitting on top of the screw, don't go fucking mad with the hammer, just a few light taps. The idea is the same as both other methods, to get a tighter fit.
