This is how I did it: I took two profiles and two Xbox (mine and my brother's) to get the achievement for my profile.
What I did was:
- I did it on sunday morning (few people playing).
- I started the search with my brother's profile and waited 10 seconds, if none opponent was found, started the search with my profile.
- 90% of the times I did this, both profiles were matched on a fight.
- The rest 10% my brother's profile found another player, hit B and go back (on both profiles). Waited a few minutes (to that new player to get bored and leave) and then repeat the process.
- The rest is just a little luck.
Hope this helps, guys!!!! Sorry 'bout my english, I'm from Spain.