If he is staying overnight, put him on your or his own room reservation and reserve Magical Express for him at least two days in advance of his actual day of arrival and of his actual day of departure.
(Sorry, he should not be in your room overnight if the room is at capacity without him.)
For a day visit he can buy a round trip shuttle ticket from Mears, I think the cost is about $30.
Now I am not sure of the procedure for reserving the trip (time wise) back to the airport via Mears' shuttle, perhaps someone else can fill this in. His pickup would be between 3 and 4 hours before his flight depending on how Mears schedules things on that day.