Go to the objects folder and find the xdp for the runway called by the facility xml. Each set point position entries determine the start and end positions of the take off roll for one aircraft. Play around with them and you can get the aircraft lined up line abreast, or staggered down the runway or anything else you like. The default max number of aircraft on the runway is 4, but if you add more "routes," each containing its own set of position points, you can add as many as you like.
Daniel