I installed two volume controls in a bathroom renovation. Pipe is CPVC. While I thought I had the pipe sufficiently clamped, there is still a little too much side-to-side play in the valves (pipes enter/leave each valve vertically). Any advice on clamping from the access panel side to deal with this twisting? I strapped them to the adjacent stud, but that doesn't take care of it. I need to lock these clunky valves into place somehow, and am even considering bracing the part that goes through the wall with ply that would be glued to the back of the durock.

There is room for a hose clamp or two, but attached to what else?

(Sorry for the confusing post without a pic.)