The rate of the rotary effect for all KB3 voices is controlled by CC# 68, so by assigning any of your realtime controllers to this value, you can change the rate.
To use the Modulation wheel:
Hold the controller button and move the mod wheel, this will switch the display to the Wheel 2's parameters, and you will see that it is set to Mod Wheel in the display. With the cursor under the Mod Wheel setting, rotate the data wheel clockwise until the value is 68, the mod wheel will now control the rate of the rotary effect on the currently selected zone.