I'd say if you can find a 3speed IGH with 120mm that gives you the range you want then go for it, get it laced up as a second wheel with some sort of fully enclosed externally routed shifter and cable. You might be able to use the same chain so switching to gears is as easy as changing the rear wheel and zip tieing the shifter on.
I'd say if you can find a 3speed IGH with 120mm that gives you the range you want then go for it, get it laced up as a second wheel with some sort of fully enclosed externally routed shifter and cable. You might be able to use the same chain so switching to gears is as easy as changing the rear wheel and zip tieing the shifter on.