You can now add Pre-Shoot Days to the calendar, then go to the Events Manager and add an event for the cast members that have still photos (e.g. Camera Test). This will display on the DOODs prior to their Start Work event simply as Camera Test (T) under the corresponding Pre-Shoot Day (Pre 1, Pre 2, etc).

Soon you'll be able to add Pre-Shoot Days in general to the stripboard.