Or…
Just get them to open the downloaded (S2) Sonos App on their own phone/tablet (or use a dedicated device that you may want to provide for them) which needs to be connected to the same local network subnet that the speakers are using, in order to discover the nearby Sonos system, however just don’t give them the Sonos account/password. The temporary visitor(s) can then use the App to play the installed music services to the local system.
Without the account credentials they will not be able to use the important administrative features such as adding/removing devices, or music services etc.
It just provides them with playback, grouping, volume control, EQ access etc.
To actually see the features the visitors will have available to them in your system, simply logout your own Sonos App from your Sonos account and ensure they will have everything they need without compromising the local system setup.