If you were to put a switch into the OBD connector, I would buy a short OBD extension and put the switch on that. You would not have any warranty issues that way - if you have that concern, as you are not cutting into the vehicle's wiring harness.
http://www.amazon.com/OBD-II-Female-...s=obd+extender
I guess I should check my ScanGauge II and see if it is doing anything similar.