Moen 3320 rough-in confusion

[Plumb Crazy]

Greetings all,

This is my first time using the forum and I hope to see a quick resolution to my "potential" problem.

I have also posted this question under the "Shower & bathtub" thread but wanted to ensure the widest audience read my post. I apologize for the duplication but my deadline to complete this project is quickly approaching!

I am installing a master shower area (for lack of a better term) with a body spray shower system. The main valve is a Moen 3320. My problem is that I do not see how I can rough-in the valve within a standard-sized wall, or for that matter, how to connect support to it.

I've seen smaller valves supported solely by the two vertical feed lines but this valve must weigh ten pounds. It is so big that when positioned where the face plate is flush with where the finished tile will be, there is only about 3/4" left before I would hit the back part of the wall (drywall).

Any input on how to mount this valve would be greatly appreciated.

Thank you!