Guys there is probably only one ground and ONE power wire in the OBD-II socket. It can't be that hard to wire in a switch.
When I asked at my dealer the other day... they did not know IF pulling a fuse would work or not (some said #74 in the fuse box behind the glove box). But they did say it would be easy to wire in a switch! Didn't I read somewhere about port #7 on the OBD-II is 12v power (continuous). I know IF I had a 1M I would be probing the OBD-II port with my VOM. I will look at this with my 135i.
I am not even sure IF removing the power source from the OBD-II port would be enough to stop one of these key fob reprograming boxes. Some OBD tools have their own power supply. I know one of my OBD-II readers has a 9v battery.