Not yet, but I did something similar. I have a headache rack in the bed and during the camping months, I run without a tailgate. I wanted to keep the backup camera, so I bought a $20 back up camera off Amazon and a plug from the Ford Dealer that matches the truck plug that the factory tail gate camera attaches to. When I pull my tailgate, I plug in my secondary camera.
I have been contemplating this same arrangement for the trailer. I would just need another camera, another plug and some wire to fit in between them. Would likely just run it down the frame rail on the trailer to the truck.
2016 Jayco Eagle HT 29.5BHDS (ordered 12/30/15, delivered 3/8/16)
2015 F-350 crew cab, short bed, 6.7L PSD, Pullrite Superglide 3300 hitch