I have no "EventHandlers" or "CreateVehicle" commands as i'm using the old OFPv1.00... Thisway i'll give you a "non reliable" answer:
DeleteVehicle your tank and then
CreteVehicle a new one in the same place of the older. Then, just
MoveIn<crewstate> (moveindriver, f.ex.) your crew. I think it works fine, but i'll leave the syntax with you
.
Remember that before you delete your tank you should remove its crew, as they might get deleted as well... Therefore just place them in a "unsightable" place and then get them back into the new tank.
I just read in a thread that a vehicle's crew is named in the begining of a mission: inside the Tank1 will be Tank1D (as driver), Tank1C (as commander), and Tank1G (as gunner). Check it out and then tell me something.