How to register a custom binding extension in code for a self hosted WCF service?

Question

I need a suggestion to register my custom binding extension for my Silverlight duplex commnication (to use PollingDuplexHttpBinding) for my self hosted WCF service.

Below are the binding details, which I got from this msdn page.

<!-- Register the binding extension from the SDK. -->
   <extensions>
      <bindingExtensions>
        <add name="pollingDuplexHttpBinding"
            type="System.ServiceModel.Configuration.PollingDuplexHttpBindingCollectionElement,System.ServiceModel.PollingDuplex, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
      </bindingExtensions>
   </extensions> 

I need add the above xml code through the codebehind into my custom binding.