trace sql without session_id and serial#

My current database so many users are connected. SQL trace is off. I need to trace a developer session. I just have osname and username. Session is not connected right now. As soon as he connects some sql fired from that session. I know how trace it after he connects I can see session info from v$session but without knowing session id and serial#, how can I trace with osuser and username only.

I cann't restart database, because so many people are working on it.

Oracle Database : 9.2.0.8
OS : Windows 2000 Received on Thu Jul 26 2007 - 02:14:15 CDT