I believe that I have found a small oversight at the end of Pothole Panic, which Rare was unaware of:
(That's a picture of the area using the European version. It works with the USA and Japan versions as well.)
The quirk must be accessed using the code: TUFFER (GBA) or TUFST (SNES)
When you're on that level, lose a Kong. Then, when you get to the point where you see the barrel (at the end, where Squitter is), Ellie is unable to make it to the barrel, even if you jump off of her.