This can be done in Custom Lobby matchmaking. I used two controllers
Versus>Custom>Online Game>Host Private
I did Allfathers Arena since it was the first map, but you can do any map. Change the game mode to gridiron.
Under Gridiron Options turn fill with bots off.
Under Weapon Substitutions in options replace all the guns with Frag Grenades.
Start the game, find the nearest nade, plant it in your goal(or anywhere), use the other controller to grab the flag and simply walk into the nade, Cheevo popped