How to register the custom binding extension for self hosting WCF service?

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C#

WCF

Silverlight4

Good Day! I need a help/suggestion to register the custom binding extension for my silverlight duplex commnication(To use PollingDuplexHttpBinding) for my self hosting wcf service. the below is the binding details which i get it form http://msdn.microsoft.com/en-us/library/cc645027(VS.95).aspx

<!-- 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>