Let's be conservative and say it's 18" of additional pipe that's needed. It's straight, so all they really have to do is tack it on. The diameter changes slightly, but they should easily be able to take care of that. Add one hanger to the back and hang the rest on the original mounts.
No reason to hack it up if it's already in his shop. Sounds like he just wants you out of his shop after having a hard time w/ the w/p.
