I will be soon changing my galvanized water supply pipes to copper for my shower in my main floor bathroom. Is there a way to change the pipe to the showerhead without cutting open the drywall? I have not opened the access panel for the bathtub yet. I guess when I do I can look up in the wall and see if the pipe is secured to the studs. I'm hoping I can pre-fab the "L" shaped vertical pipe and short nipple pipe and fish it up the wall without cutting any drywall away. Any tips would be great.