Intercept and manipulate SOAP messages in WCF
"WCF does not support the use of SOAP extensions, but it does have other extensibility points that can be used to intercept and manipulate SOAP messages. For example, you can use a behavior extension to hook into the WCF Dispatcher with a class that implements IDispatchMessageInspector."
See here a sample application (proof of concept) how to do it. Take a look especially at the :
class TraiterMessageInspector: IClientMessageInspector, IDispatchMessageInspector
class CustomEndPoint : IEndpointBehavior
and the configuration in web.config