I have a custom Ubuntu 12.10 configuration (started out as a minimal installation of Ubuntu 12.04 with a number of other packages such as Gnome Shell selectively installed via apt-get and then upgraded to 12.10). (Almost) everything works just fine. However, the lock screen (Gnome screensaver) does not expose a UI to control music playback. Whenever I have Rhythmbox running in the background I cannot pause music playback without unlocking the screen. Obviously some package(s) or configuration bits are not present but I am not able to figure out what needs to be added or done in order to enable playback control in the lock screen.
Any idea what I might be missing? Ideally I would not like to install Ubuntu desktop only to get music controls in the Gnome lock screen.