Swap speedo to get better control?
 

My buddy has a Stingray and recently got into wakeboarding. He likes it, and the boat actually puts out a decent wake for an i/o at the right speed and line length. The biggest problem is keeping a constant speed, especially since the speedometer starts at 20mph.

Aside from towing based on RPMs or getting PP, is it possible to swap out speedometers and put in one scaled more to a wakeboat to get better accuracy towing at wakeboard speeds?