I fixed it the way burmashave suggested. However, it seems this method is not the complete story. As root, edit the file /usr/share/applications/hildon-status-bar/hildon-status-bar-battery.desktop and /usr/share/applications/hildon-status-bar/hildon-status-bar-internet.desktop and remove completely the "Mandatory=true" line. Now they should be selectable in the control panel.