You could probably get audio by connecting your phone to the conference call via an audio only connection and piping that through the car speakers via bluetooth.
Yes, that works. One can participate in an in-car, in motion video conference watching the video on the car screen with WebRTC call, and calling the same meeting with phone and using Bluetooth to play audio through the car sound system.
You have bi-directional audio, and view-only video+content on the screen, but no way to use the Tesla in-car camera to send your video to others.
Would be nice if Tesla allowed WebRTC to access and use the in-car camera in Model 3s.
If Tesla gets itchy to disable this, I hope (maybe) they could leave it as a feature that works as long as autopilot is operating, or (at a minimum) still allow it when the car is not moving.