How to handle client disconnect with PollingDuplexHttpBinding

Question

I am implementing a WCF service, with a Silverlight 3 client, which uses a PollingDuplexHttpBinding for communications. What are the alternatives for handling when a client closes their browser without disconnecting from the server first?

I know that it will eventually throw a TimeoutException, which I can catch, but is there a better way of detecting this?

Thanks.