You may be able to "trick" C4 logic into thinking something is happening that is not actually happening. I have a feeling this would not work, but maybe you get lucky. Build an audio switch driver with only analog audio in and out. Bind your SONOS outputs to the inputs, and the outputs to your matrix switch. Test. Bang head on table. :)

I had to do similar workaround trying to force the HC800 to never use HDMI for an audio source. There were 2 drivers C4 sent me (I could have built them myself easy enough). One took HDMI in, and only had component video out. No audio. The other had component in, HDMI out. This essentially removed the audio path from the HDMI output on the HC800 so that the C4 logic would not try to use it for an audio output. It is all trickery. Maybe some of it would be useful here.