Model S head rest is not the same design like the other cars, and I have a hard time finding a solution to put a rear seat DVD system on it. Here is my solution, you can buy any portable DVD, but the head rest mount is probably the best possible fit. I tried many others, they don't work as well. This one, I have flip 90 degree to slide under the head rest, see pic.
TFY Universal Car Headrest Mount Holder with Angle- Adjustable Holding Clamp for Swivel Screen Portable DVD Players, Black: Amazon.ca: Electronics
TFY Universal Car Headrest Mount Holder with Angle- Adjustable Holding Clamp for Swivel Screen Portable DVD Players, Black: Amazon.ca: Electronics