I've done this before but never noticed how to do it until today... well...
1.- Take both Kongs to a level with water and ground... and no Snapjaw... Lockjaw's Locker's a good choice.
2.-Go in the water and switch the Kongs, doesn't matter which one, but I suggest switching from Dixie to Diddy*.
3.- Go out from the water to the ground, and quickly change the Kongs again, if you fall a fair distance from the pit you jump from, you can switch even if the other Kong hasn't arrived yet.
4.- Quickly jump anywhere, I suggest to somewhere high...
What would happen?
Dixie/Diddy would fall in a really slow speed, simmilar to the descendant speed in the water... If you keep jumping, Diddy/Dixie would continue to fall slow, if you stop jumping, their physics would be reseted...
I have nooo idea how it happens, all I know that's a way of making it happen, I did it in my DKC2 cartridge, which I don't know what version is, but is NTSC...
Here's a video with this bug, at about 00:53, Dixie falls really slow into the water
PS: All this steps are required, if you don't switch in Step 2, but switch in Step 3, the bug won't occur...
*I suggested using Dixie since when she falls her hair is whirling, which looks really awesome