2nd Gen Front and Rear camera?

I have a 2012 with a homelink mirror with the screen and the entune nav unit which the factory rear camera is wired to. I was wondering if anyone had successfully wired a forward OEM camera to either the head unit or mirror.
Any knowledge of the wiring would also be helpful - does the camera signal pass through the ECU or go directly to the screen with a wire from the ECU to engage?

 

If I remember correctly the mirror is always getting the camera feed but it only displays when the signal for "reverse" is sent to it ... maybe from the ECU or the tranmission itself.. depending on your head unit you should be able to get the camera image cable from the camera to the head unit and then get power/ground to the camera and then the head unit would display it when you selected 'camera' or the head unit might have a signal wire that is supposed to come from the transmission that you could spoof with a switch in the dash.

 

I would like to get an "approach" camera myself. Won't bother until I replace the head unit.