They normally fly a continuous Hold over Lambourne VOR, this being the nearest one to the course. At 28,000 ft they can be direct-sight to dish transmitters at all the camera positions around the circuit. Must be an interesting hold position, above all the Heathrow inbounds circling there. From there they downlink all the signals to the TV control room somewhere. Done this way certainly for the 2012 Olympics Marathon, I don't recall if it was done before.