I don't think that you will receive anything else than a 'flat' region with the 'create region' command. It is not intended to do anything else than creating a (complex) shape (!) on the current (ACS or active) height.
I see only one solution: you might want to 'walk' through the created vertices, and search for an element at a different height but at the current coordinates. I'm not sure how such a shape behaves, in the case of beeing filled or rendered. You might run into trouble with this, and get 'ugly' screen displays.