Originally Posted by LittleFreak

I don't think that's possible to do, nor do I know any good tileset for trying that.

You could use a work around though.

1. Make the tunnel, which Jazz/Spaz/Lori can't pass because it's too small.
2. Recreate the exact same location somewhere else, but this time put some of the tunnel tiles into layer 3 so you can get through.
3. Place the frog morph somewhere and make sure you can't get to the layer 3 covered tunnel with Jazz, and not to the inpassable tunnel with Froggy.
4. Make sure that it looks like it's the same location.

Hope that helped.