Comment 10 for bug 139806

You can fool GNOME into thinking any removable media is an audio player by creating a file called .is_audio_player in the top-level directory of the device, with contents similar to the following:

audio_folders=thomas/music,unsorted/music
folder_depth=2
output_formats=application/ogg,audio/x-ms-wma,audio/mpeg

See http://live.gnome.org/Rhythmbox/FAQ