While on the demo select screen, highlight a game or video and press either "L1" or "R1" to cause the icon to rotate and reveal a code. Enter the code that is shown while keeping the same game or ...

On the main menu, yo can press L1 or R1 to flip the game monitors around. If you do this on certain monitors, you will briefly see a code. Entering one of these codes allows you to play a hidden demo.