People have had success doing this:
1.) Connect the Parking Brake lead from the hide-away unit directly to ground.
2.) Connect the Reverse-Signal lead from the hide-away unit to a switch near your seat that your can activate while driving. Connect the other side of the switch to 12V power.
3.) Loop the video output from the top of the hide-away unit into the rear-view camera input on the bottom of the hide-away unit.
4.) In the AVIC-N2 initial setup screen, turn on the rear-view camera feature.
there will be a text message at the bottom of the screen that's meant for actual rear-view cam use, something to the effect of "CAUTION: IMAGE MAY APPEAR REVERSED