Player 1: Sit at Multiplayer main menu while hovering over "Public Match"
Player 2: Go to "Main Menu", click on "System Link" and hover over "Create Game"
Player 2: While hovering, press Y and SPAM A join player 1. If done right, you will see a black screen and will have NO rank and a 0 to the right of your gamertag (Player 1 will see Player 2 join and leave immediately)
Player 1: Invite Player 3 and then click custom games when Player 3 joins your game
Player 2: When player 1 is in custom games, press B and go to "Xbox Live" and wait.
Player 2: Invite player 3. When player 3 joins, invite player 1 (You will see them join and leave immediately)
The player that shows "Waiting for 5 more players" is the host. this player will load up the modded CTF game and add 9 ENEMY bots and 2 FRIENDLY bots.

I didn't find this out!