ExpeditionJim, I would think you could tap into the reverse signal wire going to the mirror and put a switch in. If someone had the wiring diagram it would be really helpful. I thought I read somewhere that the camera is on all the time anyway so the mirror may just be looking for "ground" to show the image.
nckracer, I think the Ford LOCKPICK works on the 2009 and up Expys that have the rearview image show up on the NAV screen. The 07 and 08 had it show up on the rearview mirror so I dont think it would apply here.