When I lived in Atlanta, one of the local TV "journalists" was going to run a marathon for some charity. What really happened was, the TV van dropped him off about mid course then parked the cameras about a mile down. He ran to the van (long enough to work up a sweat) and they filmed him going by. They then picked him up and dropped him about a mile from the finish, and again, filmed him crossing the finish at just over 4 hours.
They will probably do the same thing here.