As far as I'm aware, there is no Z direction for a UV. for that matter there is no X or Y. only U,V. This is at least one thing that is consistant between all the CG software.
As far as I can tell, what you are trying to do can be done by stretching or squashing the polygons.
I don't know the specifics of how to in Maya, I'm a Lightwaver.
althow this is a forum for a challenge, you should probabbly post this in a different area.
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