On controller 2, set the Credit limit to 9 and start the game. When player 2 starts launching grab controller 1 and press START. Let the player 2 ship die and player 1 will now have 16 credits.
At the title screen, choose Adjust Settings, then Miscellaneous. Then select Credit Limit and press Square, X, O, Triangle simutaneously. Credit Limit will change to Free Play.