Joking apart, dont think you should try drilling it out, the drill usually slips off the harder screw and heads for the softer ally casing (Especially if youre using a hand held drill). You need to remove the rest of the screws, Thats ANTI clocwise , remove the casing and hope that theres enough of the old screw to get hold of with some mole grips. Put the broken off screw right at the other edge of the molegrip jaw, this will keep the jaws parallel so they wont slip off...Good luck...And good luck with your adventure