Please read the whole thing for the two variations to this method.
If for whatever reason you'd like to farm this faster (even faster than having your boosting partner commit suicide on each map) just play ARENA with a boosting partner (no bots) and haver boosting partner press the start button and select "quit" from their start menu. Doing that will take them out of their game (obviously) but will leave you in scrolling through each map a lot quicker than if they stayed in the game committing suicide, while automatically making you the winner at the end of the round.
Just keep sending your boosting partner an invite and quitting the game once it starts. If you're curious if this has been patches in the future, just try this method, then go to the main menu, and see if the online victories are increasing or not.
Method 2 (I wish I had figured this one before I got this achievement)
IF you're interested in also working towards the "money" achievements choose PARTY instead of arena, it will be slightly slower, but if you follow the sameethod, you'd be able to grab the bonus pot for pretty much each match, building "money" while farming this achievement.
You can track your "money" in the main menu, under statistics.