All riders
 
Select "Freestyle" at the main menu. Select Sierra at the character 
selection screen. Select "Time Trial" at the race configuration screen. 
Set the number of laps to "6". Turn off all Blades, then put Edge as 
Blade 2. Start a race, pause the game, then quit the race. Press Triangle 
at the race configuration screen. Press Triangle at the rider selection 
screen. Quickly press Up, Down, L1, R2, R1, L2, Circle, select at the 
title screen. 

If you entered the code correctly, a box with "All Riders Enabled" will 
appear near the lower right corner of the screen.