Boosting this is better than the actual pvp, I had a bunch of lag issues.
Once you get into a game, invite your partner to coop so you are both in the same lobby. Then disband and search in the duels menu from the altar, hopefully it will put you in the same match.
Once there, whoever is losing jumps off the edge three times to end the match. You can stay against the same person by pressing A to rematch and switch people.
Edit: Looks like 3v3 matches do not count towards this but that could be buggy.