I am not aware of an official system other than waiting to see what flight he is in then asking for assistance on this forum..
If we base it on last years flights and your buds Low Index of 16.6 would most likely fall into flight 9. With over 1K more players this year compared to last it is hard to guestimate how the flights will will be divided.
You might want to consider alternating the use of the (1) vehicle from day to day depending on the distance to the course. Assuming that the farther you are from the course; the harder it might be to acquire a ride.
Just a thought.