When I was LE several years ago now, I recall following a speeding vehicle up to a set of Traffic Lights which turned red, the vehicle stopped at the red light and then noticed the marked police vehicle in his rear view mirror, after 2x cycles of the lights from (red ,amber, green) the offending...
Try one of those self adessive rubber pads, the type that sticks under a laptop to stop it sliding about .Stick it on the inside of the glovebox so it pushes the switch in a little further when closed !