User Inactivity/Activity Report

I need to provide our sales managers with a report that shows all users for their division and the number of accounts, contacts, and opportunities they have updated, deleted, or created for the current month.  The challenge I am running in to is that the user reporting area only contains data if the user has had activity.  There really doesn't appear to be able to provide a list of users who are not active in the system.  Essentially, we need to demonstrate which users are not utilizing the system and either spur them to action or inactivate their account.

Has anyone had to create such a report?