This is a guide to help drill the holes for my shoulder button bracket, over at sudomod http://www.sudomod.com/forum/viewtopic.php?f=38&t=3364

(please lay it flat when printing. My modeler made it stand up for some reason, it should be printed flat) It should fit snuggily in the area above the battery compartment, wedged between the wall and the lip towards the center (please see pictures). The flat end should press against the side, with the notch indicating which direction is up. The orientation is important. Then, flip the piece around for the other button hole, making sure that the flat end is against the wall again, with the notch facing up, and the chamfered edges facing the center.