Using setControlObject; where is the object?

I'm trying to build a game around 2 modest demo missions largely implementing the FPS and Racing code and objectives. The Racing mission my group coded involved driving the GG dune buggy around to 10 checkpoint flags, in order. The mission works just fine by itself, but for my project I start the game off with a Player object who can walk around (in a separate mission, separate .mis and terrain and whatnot) until he reaches a buggy which starts the checkpoint mission (via triggers placed all around the buggy).

The problem is, I changed the code so instead of just Racing-style, when the mission begins, the Player can walk around and enter the vehicle (I used the code found in this thread) and everything..but the checkpoints don't work. The mission "works" if the player doesn't enter the vehicle. I think everything would be alright if I changed it back from FPS style (that is, to implement all the functions from the original server/game.cs file into the new one, so a car is created/spawned at the beginning of the mission instead of a player), but I'd really like to keep the ability to mount vehicles for future use. Any suggestions?