Host AUs with default sidechain input: how to deactivate it?

Some AU plugins have a sidechain bus that is enabled by default. Hence, if you want to host them in a JUCE-based host, you’ll end up with two input buses, and usually you can’t deactivate or remove the second bus after initialization.
An example: Waves C1 compressor. Try to load an AU instance of it in a stereo channel in Tracktion or Waveform, and it won’t compress anything, because it will have no input signal on its sidechain bus. If I restrict the number of input buses in AudioProcessor::initialise to 1, it behaves as one would expect it on a stereo channel. Shouldn’t there be an option in AudioProcessor (e.g. maxNumInputBuses) to be able to choose your bus setup as a host during plugin initialisation? Or am I missing something?

Maybe this isn’t completely clear? I have tried the obvious plugin->disableNonMainBuses() of course, but it returns false… so I need a way to only add the main bus during initialization already.