I looked into that before and could not find a way, I did not look into aluminum rods but I don't think they are gonna get much lighter than a SCAT I beam, the lightest common affordable strong rod. I think if you got some custom ultra light pistons you could MAYBE do it but even then you would probably have to weld up the existing balance holes in the counter weights and grind off the casting protrusions on the pin side of the crank.