I can't post it on Cheats.gamez.com because I'm not a user, so I figure I'll just post it here:

On the course "Choco Island 2" There is a rather small shortcut located near the start of the course; I've forgotten where. It's a small gap in the wall on the let-hand side. If you drive straight at it, you'll shave about 2-2.5 seconds off your lap time. Yeah, I know, it may not seem like much, but if you time it correctly, you'll be about a position higher, as the others have to go on an S-curve. A mushroom or Princess turbo (the gold mushroom thing, lasts about 5 times longer) may be handy, as you're driving off the course.

This also goes for the course "Donut Plains 1"

Happy Gaming!
-3xinvert