[Angel And The Wolf]

I have a back up camera in my Prius, but I want to mount a rear view camera under each outside mirror. I regularly have to enter freeways at such a shallow angle that I can't see what is coming up in the lane I'm entering. I'd like to tie these cameras in to the OEM screen, so that by mounting a pair of micro switches near the turn signal stalk, I can turn on one or the other outside cameras by using the turn signal, but I don't know the logistics of tieing in to the display so that it will show the image from activated camera as it does the back up camera when it is activated. Anyone have experience?
BTW, the screens that come with most of these systems show those pesky guide lines, and I don't want them.
Also, I don't want to clutter up the dash with monitors.