You can do it from the browers directly. Out of the box, if you add this after the url it should start in VP9 Profile 0 direcly:
?PreferredCodec=VP9+profile-id%3D0
Haven’t manage to get any other VP9 profiles working and MaxP/MinP seems to have no effect. However, you can control the data rate with WebRTC.MinBitRate and .MaxBitRate to get a nice and efficient video stream.