I have given this some thought. I believe the best method is as follows:
1. By 2nd camera of the same type as front camera
2, Re-use a hard drive data cable used for a hard drive
3. Purchase a micro slide switch
3. Remove Nexus internal board
4. Cut out appropriate size to mount slide switch
5. Cut out section at the back of case mount camera with clue gun
6. Splice cables from front camera, to switch then solder
7. Solder rear camara data cable to switch and camera
8. Solder live feed from swich to spliced cable on pcb board
9. Insulate cables
The above will allow you to in theory to use a manual micro slide switch
to turn on and mack active front or back camera.
