I have done it But unless you are water cooling there is really no collective benefit for all components temp wise and leaving it off is better if air cooling!

Put a small 20mm x 60mm fan over the pwm fins and that will drop tems about 6c on both PWM & NB Also what I did with my Q6600 was install a Thermalright HR09 on the CPL-4-150 with Arctic Silver Lumina and the temps were equivalent to having the Fan over the PWM area