How to sync via USB with the FolderSync Android app?

This task refers to the FolderSync app version 2.5.4 – the paid version, though it may work with the lite version too.

It seems that this is not an intended feature currently, but it is possible. Instructions:

1. Enable USB tethering on your Android phone.
2. Connect the computer to the USB network connection (while disconnecting it from wifi to make sure indeed the USB connection is used in this test).
3. Look up the computer's IP for this connection, and set up an account (here, SFTP) in FolderSync accordingly.
4. Create a folderpair in FolderSync, and make sure that you check "Use Wifi" for the connection to use.
5. Make sure wifi is enabled on the Android phone and connected to some network. (Sadly, the folder syncing via USB hack only works when the phone is indeed connected to a wireless network, even though the actual data goes via USB of course. I guess "connection" means "wlan0 has IP address", not that an actual Internet connection would be needed. So if you can find a way to set up a static wifi connection to a base station with an invented ame (that is not in range of course), it should be sufficient to make FolderSync work.)
6. Open the folderpair entry in FolderSync and click the "arrows in circle" button to trigger immediate syncing. Should succeed now.

With wifi disabled (or enabled but not connected to any wifi network) on the Android phone, the following error message will appear: "Folderpair not synced because syncing is not configured for current network type or network is not available".