Brian over on T4R.org makes a backup camera override harness for 5th Gen 4Runners. Maybe contact him to see if he has fiddled with making one for the 200?
I had one in my 4Runner, and it was easy to install and worked great. Just plug and play behind the head unit, plus add a switch. Maybe that's not quite as easy with the four cameras on the 200.
View your factory backup camera at anytime with the press of a button! PLEASE CHOOSE OPTION FOR STYLE TO ENSURE YOU RECEIVE THE CORRECT HARNESS. Our Anytime Backup Camera Harness allows you to view your rear camera at any time. The harness will plug directly into the back of your factory in-dash...
www.anytimebackupcamera.com