I asked the maintainer of the last.fm plugin if it would be possible to scrobble
Internet radio streams and he replied with the following:

  I think it's possible.

  Take a look at
  plugins/scrobbler/rb-scrobbler-plugin.c::playing_song_changed_cb():

         if (type->category != RHYTHMDB_ENTRY_NORMAL ||
             type == RHYTHMDB_ENTRY_TYPE_PODCAST_POST ||
             rhythmdb_entry_get_string (entry, RHYTHMDB_PROP_PLAYBACK_ERROR)
  != NULL) {

  You have to change that to:
  if ((type->category != RHYTHMDB_ENTRY_NORMAL || type->category !=
  RHYTHMDB_ENTRY_STREAM) ||

  And you have to change the invocation chain down to scrobbler_start()
  because you can't provide a file name for songs from streams.

I have asked him if he will apply this upstream but have not had a response.

Would you consider adding this functionality to the Debian package?