Striped screw heads suck. Sometimes a drop of super glue on the end of the hex key will be enough to loosen the screw. Be careful to not use too much as super glue can get everywhere and make a bad situation worse. Alternatively you can use fast set JB weld.
Worse case scenario, try using a dremel to cut a slot in the screw head and you can turn it out with a flat head screwdriver.
Good luck!