The point is not finding a way to plug in a device or any other shortcut.
It's all about convincing Spotify that we would be happy to use their free service also through our Sonos system (with all the advertising or whatever they consider is necessary, even with some differences in the service if they think it's a good strategy) and that would allow them to increase the number of users. At the moment their policy with Sonos seems to contradict their general approach. Probably because they think that if you spend money for those speakers you can afford a premium profile, but I would reconsider that idea ;)
I still cant understand why you need a paid subcription to listne to Spotify on Sonos. The ony benefit to a subscription is have access to your saved music when off line. You cant acces Sonos off line!