Support for custom scrobbler url to last.fm plugin was added in version 0.3.2.
1. Open the Preferences dialogue in the Edit menu.
2. Select the Plugins tab.
3. Select last.fm scrobbler in the list.
4. Click the Configure button.
5. Change Scrobble URL to: http://turtle.libre.fm
6. Close the dialogues with the Ok button and then the Close button.