Might be able to get something like this in and working. Some RF cameras and receiver + standard cam into the box and out into your headunit under the reverse camera input.
Car 4-Way Video Switch Parking Camera 4 View Image Split-Screen Control Box W7U5 194982745254 | eBay
There are a few 'car launchers' for android as well that take over the whole environment to customise the OS, Im going to have a play with a couple:
Car Launcher Pro
CarWebGuru
FCC Launcher
Nova Launcher

