you could use a left crank from a tandem to solve the pedal threading issues - TA (amongst others) do tandem chainsets, and can often be bought as single arms e.g. if you bought left stoker (person at the back of the tandem) and right stoker then you could run chainrings on both. Some examples of left hand drive on FGG:

www.fixedgeargallery.com/2004/d/walter.htm
www.fixedgeargallery.com/2004/e/pmiller.htm

Olly