Had a though about the duelies... I honestly don't know if its good or not but i will throw it out there anyway
What if on the inner set of tires you ran a slightly taller tire then the outer set? that way you would have less rolling resistance but the out set could act as an overload tire for when you carry weight? I suppose with duelies the weight is distributed over a larger area so maybe you have less RR anyway? I don't know but I am sure somebody here does!