Our students who are on reduced timetables go to the library to work. Usually this is supervised by the dedicated librarian but when she is absent, it would be useful to add her absence to the Cover Manager to allocate the staff covering her. She does not have a timetable so her periods will need to show for the day she is off work.
The workaround I use to allocate Operations staff cover is to mark them as teaching staff within their HR profile, they then appear in the 'free' listing in Cover. Your HR Manager may not appreciate it though!