ASP.NET Session Timeout Notification In Silverlight 4?

I have a hosted Silverlight 4 application. My task is to notify a Silverlight user when his ASP.NET session is about to expire with a simple dialog box, saying something like "Your session is about to expire, would you like to reset the session?" with two buttons [Yes], and [No]. When the user clicks [Yes] I would like to update the ASP.NET session, otherwise I would just let it expire. What is the best methodology to use here?I've taken a look at different forums, and most people just simply poll the server every-so-often from the page hosting the Silverlight application. This wouldn't do for me. I thought of creating a singleton DispatcherTimer that would start on Silverlight application startup, would fetch Session.Timeout value from the server using WCF and would run for (Session.Timeout - some delta) minutes. When the timer expires it would pop the notification window. Moreover, since this notification window should only pop after a period of inactivity, I'd like to reset this timer every time a WCF call is performed (which essentially defines activity).P.S. I'm also planning on doing something similar for Forms timeout.