Needed - historical report of number of employees in each pay period including those on hold as well as those paid.

Our auditors have said there is a new requirement to report the average number of employees on the payroll for the year, and they need this info for 2015 and 2016. The trouble is that we have many casual employees who are on hold each week/month and they need to be included as well as the employees actually paid. I can't find any report that will give me this. I need to run it for each pay period to get the average. I've tried the employer status report but although it gives me the right information for the current period, it gives me nonsense for historical periods. Can you help?