I can't use these to grow bigger in Waterloo world, I punch them, they pop, but I can't seem to be able to jump into the champagne stream, I just miss, sort of get pushed out or end up grinding round the edge of the hole. If I jump then punch downward (ony way I knw 2 do this) I simply fall off the cork. This is a right pain, anyone got any tips on how to do this?

You need to levitate. If you do the Levitation then punch near it. As soon as you land, jump and use psi-float.