With this posting, the cat is well and truly out of the bag in the field of do-it-yourself machine guns. It seems that with a pair of pliers and a wire cutter, one can fabricate an auto sear that will convert your AR pattern gun to a real machine gun and none of that flakey bumpy stock nonsense.
As I read this your semi-auto gun will be externally identical to all the others. The "switch" is the piece of coat hanger wire that requires that you push the take down button, open the gun, drop in the wire and close it up. Not as fast as having an external switch to do it, but just as effective.