If this hub is expensive, you could take a regular hub and have any machine shop turn down and thread the left side on a lathe. It would probably be surprisingly inexpensive, especially if the chap is friendly and you explain the intended use.
The other possibility is to use an intermediate hub with double track cogs(both sides) as a jackshaft, mounted on a rear rack, then have the RH drive stuff (w/gears) run from the hub on the rack to the RH side of rear wheel. THIS MAY sound like a lot of fabrication, but if you get in touch with your local tallbike/mutantbike club they will likely be happy to do it on a volunteer basis. These folks are usually pretty civic-minded in that kind of way.
I'm glad the 3X I broke my ankle it was the left one!