Easiest way in my opinion is to do this without two controllers. If you have a buddy to help, then obviously that works. However, for those who just want to knock this out themselves here's what I did.
Level: Temple
Game Type: Challenge
3 Bots
Once the match starts the flag will appear. Do not worry about the flag if it appears near the top of the level. You're looking for the flag to appear at the bottom of the screen. Once it does, allow the enemies to make a push for it. You need to let them get close to capturing it. Be wary of the challenging mode horde as some enemies can really start to pile on which makes it hard to kill them before they capture. Just screen wrap to the opposite side and once they are working on capturing warp back over and wreck shop. I hope this helps! Should be done in a single match, no prob!