Has anyone figured out Control Buses (Audio Modulation Plugin)?

How do I use modulation parameters on submixes?
I get how I can use audio modulation/Modulation parameters to control volume, on a submix (modulating the volume of a submix via a modulation parameter), but how do you control, say, the filter freq of a submix? If I create a submix effect preset (filter), there is no section to modulate that via a modulation parameter.

Thanks