Have you ever been waiting to board FJ and noticed a large gap between benches? That gap is left by the bench on the stationary load side. When the group on the stationary side is loaded properly and ready to go, their bench crawls to the end of it's platform and waits for it's gap to return. When it's proper space returns, it matches up with it and joins right in where it should, with no slowing down of any other benches. The guests start right into the floo network sequence and then the bench returns to the secondary station during the final floo network.