There is no such service currently. 
 

Sonos doesn’t pre-announce what they’re working on, but you may want to read 

and get in touch with those people to see if they’re able to answer your question. 

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.

If you went with this plan, the guest would not be able to add their music service, nor remove it when they leave.  It might be best just to have guests play their own music via airplay, or casting if the streaming services offers it.  They would not really need the Sonos app at all, just WiFi access.

I would check in with Sonos pro/commercial services still though.  I suspect they will have better options.

Not being able to use their own music service account (most likely Spotify) is a slight minus, but even so this sounds like a workable solution for a Sonos setup in a holiday let situation.