It wouldn't take too much effort to put a row of pay barriers next to the car park ones for the exit route, which will be their final location but there would be an issue with lorries that use this route to exit the various building sites unless a temporary wide one was put in just for their use to get them off site.
It will probably have to happen soon when the first part of the new drop off area opens as there will then only be a single lane that loops around. At the moment there are 4 lanes with a barrier each.