Logging than One sleep period on a FitBit One

Hi, I have a quick question.

I am a shift worker, and I would like to be able to log my erratic sleep patterns which sometimes include sleeping most of the day, and then going back to bed the same night (after a night shift but preparing for days a couple of days later) or Sleeping all night and then going back to bed at noon to prepare for a night shift.

When I try to log my sleep, it tells me I have already logged sleep for that day, and offers me no other options to add it. Am I missing a secret "shiftworker" or " custom sleep" button? It would be very helpful if I were able to track my sleep to keep myself on track and make sure I get enough sleep.

Kelly