Connecting an AudioProcessorParameter to an external processing class?

Say I made a simple class that stores a floating point gain member. How would I get that gain to reflect changes of a gain AudioProcessorParameter located in the main processor? I tried using an AudioProcessorListener, but it doesn't work with automation because the host doesn't seem to call audioProcessorParameterChanged.

Is there a simple way to make a connection between these things? Can it be done without the external processing class knowing about specific parameters in the AudioProcessor?