sorry i havent got time to test this,but i think this may work
u need to name all your cars (eg car1 car2 car3) and a unit, eg unit1. then in a script, try something like
unit1 moveindriver car1
unit1 action ["LIGHTON"]
unit1 moveindriver car2
unit1 action ["LIGHTON"]
and so on. it wont be instant, but should be unnoticeable. if it works at all that is
(if u wish to refine the script, u could use an array of vehicles, and use "array1 select X" etc) but thats not necessary, unless u have like 20 vehicles, where it becomes a real drag to Ctrl+V all those lines!