While the previous 2 solutions will work, I will share what I did for this achievement.
Start as many private Online Associations as you can. I believe you can have 3 running simultaneously. I chose the Heat as the user controlled team in every one. Start each season. Now, this is the hard part that gets tricky....
Just log in to each one about a month later. The achievement popped for me as soon as I loaded one. I didn't play a single game, but "won" the Championship in 2 of the 3 I had.
Sure the other guides ensure you winning, but seeing as to how this game will take you longer than a month to complete, I suggest you try this early on. At the very least, for those of you like me who started this with the intention of logging into the mode a month later and yet forgot about it for 3 months or so, just know you should log into your already-started mode just to see.
tl;dr: you don't have to physically play the game to get the achievement.