Hey Armstrong.
I think there's really no other way but to 'simulate' it ;D make belief
make a wp for the unit you want to be in when the mission starts and put this in your
init.sqs file
titlecut ["OMG the screen is black!","black out",0.00001]
~10
titlecut ["W00T! I'm starting inside a moving vehicle!!","black in",7]
with choppers you select the 'flying' from the special field in unit menu.
or
you might want to play around with the unitname setvelocity [x,y,z]
in your init.sqs in addition to that titlecut hat trick
I'm using this in one of my missions and looks ok