Easy - he chucks the end of the shaft and orbits the lathe around it, ha ha. Na, that's exactly what I was wondering. I'm guessing it'll be cut n welded once he sees it, especially for $25. Hey, maybe the fellow has nothing else to do and likes a good challenge.
Let's see, a CNC mill and a threading cutter might do the job but chances are he'd end up without thread all the way to the bottom of the stub causing the knob to not run all the way down. But if he has the right threading die, he could chase it down. Other than that, I don't know how someone could take any other approach than cutting & welding.
Looking forward to the pics!