Set up a custom CTF match with your team set to 5 players and the enemy team set to 1 player. Set the time limit at 0, frag limit (which means capture limit, in this case) to 3, and the difficulty set at the lowest level on the difficulty slider. Simply fly directly to the enemy base as quick as possible (shooting the enemy down on your way there), fly low over the flag to pick it up, turn around, fly back to your base (shooting the enemy down again), capture that flag, and repeat 2 more times. This will not count if your teammate captures the enemy flag (which they rarely do).
You can also set the capture limit to 5 and try to get the Flawless CTF achievement at the same time.