absolutely it's possible.
you would first need to attach a
get in eventhandler to the chopper. that would activate a script. the script would check to see what position the person getting in got in to. if it was the driver's seat, the vehicle would have an action added to it, via
addaction. you would also need to attach a get out eventhandler to the vehicle so that when the loon gets out, the action is removed.
the action added to the player would call a script which would check if the vehicle is in range, and do the attaching of the vehicle. it would also remove the "attach vehicle" action and add a new "detach vehicle" action.
to see something similar in action, take a look at
this tutorial.