triggerhappy is right,
For example, we have two choppers, called heli1 and heli2
In the at activation field of waypoint for heli1 you have to write:
[heli1] exec "rappel.sqs";
In the at activation field of waypoint for heli2 you have to write:
[heli2] exec "rappel.sqs";
Be sure you have the last version of the scripts (Search the topic) because the first version may don't work with two choppers that make rappel at the SAME time, due to the use of global variables. (this is already fixed).
The script is no mp compatible at this moment, working on it
I've edited this post, because I wrote that you have to write the code in the init field of the chopper, and is in the waypoint .. .sorry :-\