We have a new home under construction and we are considering putting a 20" long horizontal shower arm for a 10" rain shower head. Our general contractor feels that such a long shower arm is not feasible. I am exploring whether we could make this work.

I assume that there will be a drop ear elbow, a nipple, shower arm, and the shower head (connected in that order). Please assume standard part dimensions for drop ear elbow and nipple.
a) Is there a convenient way to attach the drop ear elbow more rigidly to the 2x6 cross brace? Would it be helpful to further clamp the drop ears with small metal bars to the cross brace?
b) Would the threaded joints between the drop ear elbow and the nipple be strong enough? Is there a way to provide additional support to the nipple - by a bracket perhaps?
c) Will the threaded joint between the nipple and the shower arm be strong enough? Are there brackets used to provide additional support to shower arms?

Thank you in advance for your attention and I would really appreciate your comments.