Log Username in RAS Event ID

We are trying to create a report that reads the login and logouts of our RAS users via the Event Log, then calculate how long they have been online. Unfortunately, ALL the RAS event IDs in our System Log (event id 20017 and 20019) list the user as N/A. How can I get the actual user to appear? This is for NT 4.0 Server SP 6a. Thanks — Mike