Until Sonos does anything with Google Home you are kinda out of luck on that ask. You could create a virtual switch that turns on/off and use rules to stop/start sonos through the custom commands. Outside of that you may want to reach out to @stephack as he has some interesting solutions to other Sonos limitations.
<sorry @stephack but you really need to release that awesomesauce you have hiding. >
I worked it out. Created virtual switches named after my oft-used groups (House Sonos, Downstairs Sonos, Upstairs Sonos and Office Sonos) Created Rule Machine triggers for these switches to STOP or PLAY selected Sonos players and shared the switch with Google Home.