Would it be possible to create "adaptors" from mild steel (flat or angle) that could bolt to the outside of the existing dropouts with spacers/washers to widen the OLD? Perhaps extending straight back? It would increase the wheelbase slightly but not change headtube angle. It might need another smaller bolt to prevent rotation around the larger bolt: perhaps in the square hole that is already there?). This wouldn't be real pretty but it would not alter the frame and dropouts much at all.