This can be done with a bit of practice in Training Grounds. Select the first Japanese training mission and select the G4M Betty as your aircraft. Sink the AK and then circle around as your bombs recharge. Keep an eye on your tactical map and you will see the replacement AK spawn at the second island and pass very close to the carrier on its way to its anchorage. Time your bombing run correctly and you can hit both the carrier and the AK with the same group of bombs. The battleship is another good one because is very large, but it takes a lot longer to sink it and as such it takes much longer to get an opportunity to try the Double Whammy.