On the title screen, press: Down, Up on analog, Down, Up on D-Pad, Down C, Up C, L Button, R Button, Z Button, Left on the D-Pad, Right C, Up on analog, B Button, Right on D-Pad, Left C and then Start.

If input correctly you'll hear Slash cheer.

This is an extremely useful cheat for running the "NG+, All Races" category as well as ILs. It essentially removes the need for a controller pak entirely (except if you want to save your ghosts in ILs).