Mocking WCF OperationContext RequestMessage for Unit testing

I am trying to unit test a method that takes no parameters, in a WCF service that issues different HttpStatusCodes based off of a web request message body.

The main issue I am having is that I can't figure out how to inject the message body into my unit test.

This line is where the method gets the message.

Stream request = OperationContext.Current.RequestContext.RequestMessage.GetBody<Stream>();

Is there a way to mock the RequestMessage so that I can test different message scenarios?