I kind of like Ben's idea, because that actually did happen during World War Two. However, they were "VERY' limited in how they could move in the cockpit (unless it is larger than a single seat aircraft of course

-) If it is a single seat aircraft, then when the player types '.rescue name' and joins 'names' plane, the control deflections should be approximately cut in half to mimic the 'space' constraints and movement limitations in the cockpit (but not for the throttle). If they both make it back to base, the rescued pilot receives normal credit and the rescuing pilot receives a 5 point perk for rescuing a team mate. Of course, for the '.rescue name' command to work, the vehicle/plane you are joining would need to be stationary for the command to work.
For larger aircraft, it would be the exact same as above, except there wouldn't be control limitations. Of course, the added weight of the person who joined (average 200 lbs with gear?) should be added to any plane the rescued pilot joins.
I would also make it so that a C-47 (And a Ju-52 and Catalina, if we ever get them) could pick up 10 players. Until we get a Catalina, I would make it so a PT boat or LVT could pick up a pilot as well. Of course, GV's could pick up players as well.
For vehicles with available 'gunner' postions, I would make it such that, if not already occupied, the rescued person would occupy those positions.