The external storage feature does not sync files and folders. So if you access your files via web hosting on your local storage (at home), the files will always go through your residential internet connection.
You can’t use it because it is not implemented yet.
What you can do, use a local folder as external storage and use other sync processes (btsync or others) to keep your folder and the remote one in sync. But running own sync processes probably won’t work on web hosting.