1) place a helicopter in editor, set it "Flying" and make it's pilot playable
2) place a sling-loadable vehicle with player as a driver (or place a player as a unit somewhere nearby to watch)
3) place a waypoint for the helicopter to sling load the vehicle and fly somewhere with the sling loaded vehicle
4) play the scenario and wait until the helicopter picks up the vehicle
5) while the chopper is flying make a unit-switch (press U) to the helicopter's pilot and watch what happens.