I don't think that a tandem hub, Phill Wood or any other hub is going to work. This thing has an 450W electric motor attached to the rear wheel. I think his only choice is to take the thing to an expert wheel builder and have him redo the whole thing with new spokes. If you've broke four spokes the rest of the spokes are probably toast as well. If you don't replace all the spokes you'll just continue to break spokes. You are better off starting from scratch.