While Your looking for the hex wrench/bit, put a drop of penetrating oil on the screw/screws, and let it soak. This often helps. If that fails, this is a case where Left Twist drill bits can be beneficial. The bit grabs the screw and backs it right out. A very small one would be needed for Your application. But if You have to drill those screws out with a regular bit, no great loss. A trigger shoe is not absolutely necessary.