To remove the headrest, raise them to the very highest point. Then about 6 inches or so down from the top of the seat, there is a button that is hidden behind the upholstery. It is on the left-middle side of the seat directly below the left headrest metal tube. Press this button in and then raise the headrest by hand. You will have to run the wires somehow, but I'm not really experienced in it. Normally, wires are run down one of the headrest tubes, but I don't know if the stock headrests have hollow tubes.
Please keep me/us updated on this project, because I plan to do this eventually, and I would rather not spend the money on the prefabricated headrests with monitors built in.
Martin