I can do this also and there is a little more to it. V1.00 C3+C3C w/PTW
1. Using any unit that can normally be air-lifted, move into a airport/airbase. Give the "go to" command followed by the air-lift command, you'll now be able to drop said unit ANYWHERE, including water tiles and tiles that are currently occupied by a rival civ.
Landing in water leaves the unit(s) stuck there until you bring a transport, etc. over to them at which time they'll load as normal.
Landind on an occupied tile w/rival unit(s) seems to have no effect, as of your next turn unit(s) move as normal.
2. You can do the same as above with Paratroopers by going to airport/airbase, give "go to" command followed by Airdrop command.
But landing in water tiles or already occupied tiles results in "Air drop failed"