Okay guys, here is how you achieve the glitch.
First a warning, it's pretty complicated. You first make 20 created players (the games max) and put them on whatever teams you want. Then you take 15 of those created players (If you try to put more than that on a team the game will freeze) and place them on a created team. Write down the names of the 15 created players and there respective teams you put on your created team. Then go find each of those players on their original team and edit them into a new player. Boom you now have 15 additional created players all on one roster file.
Now to get all of them into the Association Mode, you need to do a fantasy draft Association. The draft will pull players from all teams in your roster file, including the created team. Then once you finished the fantasy draft you start the season. Make sure you have at least one created player on your Association team that was made by editing one of the original 15 created players. Export your Association team (under the save menu in Association Mode) and your ready to experience the glitch. Load your export team and play with them in practice or exhibition mode. Then have fun laughing at the sights.