Bonus Teams
Select exhibtion mode, then press L2 + R2 to unlock the Dinger and Islander teams. If entered properly, you'll hear a sound.
Austin Dingers in Batting Practice
select batting practice from the main menu. Highlight Derek Jeter and hit X. On the Player Select screen, press L1, R1, L2, R2 simultaneously. After doing this the Austin Dingers team should appear and the players will be selectable.