Install a shower head from attic?
Is it just a shower or is it a shower / tub? 

The water drains back out of a shower / tub combo stand pipe. So it would not need to be pitched for drainage.

A shower-only stand pipe will hold the water all the way up to first 90° even if it is pitched. You could add a drain valve / foot washing valve down below but you will always have to remember to drain the stand pipe after each use.

An alternative is to install a rain head shower that is entirely contained within the shower. 

On the down side, these normally need the hot and cold feeds to be roughed in exactly the right distance apart and then they are surface mounted. So you would need to tear off the front wall of the shower to re do the feed pipes.

On the plus side, you would not have to go up into the attic to work and will never have to worry about it freezing.

Good luck!