Are you free handing now? If yes, just use a long angle iron and drag the torch along side or are you talking about something with wheels to hold your torch and drag along? You could also take some round tubing the approx. OD of the torch body for the torch to slide into. Drill a hole in the side of the round tube and either thread or weld, braze a nut and just tighten the screw to secure the torch. Now, you either add wheels to the side extending a little out from the tubing and add two wheels. Get a piece of angle iron and use that as a guide. The holder should keep your torch tip height correct and drag the side of the wheel against the angle iron. There are many ways to make this holder and they even sell one if you don't want to design and make your own.
Mahalo,
doogdoog
Mahalo,
doogdoog