How to enable specific users to use specifics veichles when playing ONLINE

[goaz 11]

The question is quite simple: I have seen that on some servers only members of a specific clan are enabled to flight chopers or driver specific veicheles.

As I'd like to modify my domination coop mission by doing the same as above explained, do you have any idea how can I manage to do that by allowing only my clan mates to use choopers??

Thanks in advance.