That currently is not possible, but wouldn't be very difficult to implement as I had it in mind from the beginning. Inspiration could be the Dropbox integration:

Client-side model:

https://github.com/jakubroztocil/cloudtunes/blob/master/clou...

API endpoint: for local files, it could simply serve the file:

https://github.com/jakubroztocil/cloudtunes/blob/master/clou...

Plus it would also need indexing, configuration, and to introduce a new media type across the app.