I used to own a Yamaha and the forums are rife with all kinds of crazy stuff to make a surf wave behind a Yamaha. Personally, the only thing that worked was putting so much weight on the back corner that I was worried the engines would explode at any minute. The pocket was very small but surfable.

One of the experiments everyone tried was additional shapers. In almost all cases multiple shapers either tore off or actually messed up the delayed wake effect caused by the primary shaper. My guess is that additional shapers would not have any effect. A larger shaper or different shape might.