Another Session problem!

Hi there!
Let's say I am opening a child window on click of a button in a page. Let's assume the session.timeout=20.
When the user performs operation in the child window for more than 20 mins., the parent window's session is expired. Just before a session expires, I am redirecting any page in my site to the logout page. That means, in our case even if the user is doing operation in the child window,(since parent window is idle, he is logged out). Is there any way I can re-write to the header of the page, without refreshing? Or anyother solution is welcome.

Please help.