I think the approach is a little off. I am guessing you want to find out who changed what. There's a good chance this person can seriously screw things up, so I would not give them permissions to do that. You can create a procedure that is a proxy for sp_configure. This procedure will do your logging and maintain a whitelist of things your user can do.
If you don't want to go through all that trouble, and you still want to allow this user to mess things up, here's a post with what you want: http://www.sqlservercentral.com/Forums/Topic780731-146-1.aspx