Screenshot of the Sonos Plugin in action.
1) Create New Scene
2) Call it 'Play Sonos' - or go with what ever you want :-)
3) Go to the Advanced option/tab
4) Select the Sonos Living Room device (or what ever you've called it)
5) Click Add
6) Then from the drop down options list created below, Choose 'Setfiletoplay' and enter in the full location of that file on the NAS (pus I always ensure it's one Sonos can see too) -e.g. //192.168.1.10/media/Music/Mp3s/Changes.mp3
Now you have selected the file, you now need to tell the Sonos you want to play it
7) Select the Sonos Living Room device again (or what ever you've called it)

Click Add
9) Then from the drop down option list created below, Choose 'Play'
10) Confirm Changes & Save
Now you should have a scene that once run, will play the track you've selected.
* Interesting to note, the above will bypass the Sonos queue process and will just play the selected track only/
* if you know the length of the track being played you can set a delay to occur e.g 3.45mins and set another file to play - that seems to work well.
* The above avoids any use any coding, as I'm still learning so i hope the above helps
Screenshot below
@guessed - having this on the wiki would be a huge help, a picture tells a thousand words as they say :-)