A fast repetitious setpos of the helo depending on the position of the pulling vehicle and the helo old position. So the helo is allways in the same distance from the vehicle. And the setdir could be used too, to face the pulling vehicle.
But the thing connecting the vehicle and helo would be invisible. Maybe it can be simulated with a lot of small dust thingies in a line, created all the time, but would possibly create lag.