Ok I still don't quite understand what you need to do but because you are using a Nurbs Surface that is UV 0-1 you can use the pointOnSurface command e.g.

float $pos[] = `pointOnSurface -u $u -v $v`;

this will give you the position in world space of the point at that UV coordinate. You can then just get the Y component e.g. $pos[1] and use that. So if you now base you shop's movement on the UV parametres you can move objects around the surface very easily and you can always query their Y value.


A