Pause the game and then you may enter the codes:

Left, Left, Down, Right, Left, Right	Tom Gadget listed on Gadget Grid
Down, Down, Up, Down, Right, Left	Time Rush
Left, R1, Up, Down, Up, Left	Restart Episode
Down, R1, Left, Right, R1, Down	Warp to Episode 1
R1, Left, Right, R1, Left, Down	Warp to Episode 2
Up, Left, Right, Left, Down, Up	Warp to Episode 3
Up, Right, Right, Up, Left, Left	Warp to Episode 4
Left, R1, Down, Down, Up, Right	Warp to Episode 5
Down, Up, R1, R1, Left, Down	Warp to Episode 6
Left, Left, Left, Down, Down, R1	Warp to Episode 7
Down Up, Left, Left, R1, Right	Warp to Episode 8
Right, Left, Up, Up, Up, R1	Tutorial

Thanks to Revolution readers fiddler-styx and Foxxorz!