Bluetooth receiver connected to Sonos?

I am one of those dumb people who found out post-purchase that Sonos supports streaming services, and does not function as wireless speakers for whatever’s playing on my mobile device.

I have a lot of specialty audio files not available from Sonos-compatible streaming services I’d like to play over my Sonos speakers.

Would a workaround that would enable me to play whatever I happen to be playing on my mobile device over my Sonos speakers (assuming there isn’t a Sonos app for that service) be to buy a Bluetooth receiver then hook it up like any other kind of audio receiver to one of the more expensive Sonos speakers that connects to receivers...or does that configuration only enable Sonos to hijack the speakers of your hi-fi setup?

In short, is there some sort of way to insert an audio signal from my mobile device into my Sonos system?

(Please don’t respond to this question with rationalizations about how Sonos’ ringed fence is awesome. Perhaps it is. I’m sure it’s simply amazing. I’m just looking for resourceful solutions to my not-at-all-unique problem.)

THANKS!