Ideally what I'd like to do is pull the PWM control from the fan header on the GPU, and put that into some kind of controller to adjust the speed of the pump. The pump does not support PWM, though.

Model VSM-CA3 modulates the speed of motors in fancoil units, fan-powered VAV terminal units, fan filter units, and other air-moving devices. The controller provides modulating control of AC induction ...

Refrigeration Service Co. customers appreciate the energy savings (Figure 1) achieved due to reduced power, said Dieffenbach. Using the controller results in approximately 16 percent energy-efficiency ...