Permanently Muting Sonos One to use as Air Play Injector

I think I may need to permanently disable the speaker drivers (!) in my Sonos One but am hoping someone has a better solution to the following problem: I have only one Sonos device, a Sonos One, which supports Airplay 2. I play music directly to it over Airplay2 from the Apple Music app running on an Iphone. I group my Sonos One to various other Play:1's and Play:3's around the house: the Sonos One is in that sense the 'injector' for the whole house. I want to be able to listen to music on, and only on, my Play:3's in the Living Room, so I group Living Room with the Sonos One, and mute the Sonos One. That works fine. The problem comes when I increase the volume using the Iphone's physical volume control. That increases the volume of the {Living Room + SonosOne} group, which unmutes the Sonos One. So I end up with music playing in two rooms rather than one. The only way I can think of around this is to hobble the Sonos One by cutting the wires to its drivers, so that it is permanently muted. Surely there must be a better way! (Obviously I am aware that I could use the Sonos App on the Iphone to raise only the volume of the Living Room speaker and keep Sonos One muted, but I would rather not do this for the sake of simplicity for folk unfamiliar with that app).