How to set the default RequestFormat for a WCF ServiceContract?

I'm writing a web service that has a lot of methods. They are all set up similar to the following:

[OperationContract]
    [WebInvoke(
        BodyStyle = WebMessageBodyStyle.Bare,
        RequestFormat = WebMessageFormat.Json,
        ResponseFormat = WebMessageFormat.Json,
        UriTemplate = "x/y/z")]
    void someMethod(int x, int y, int z);

What I want to do is just set the default BodyStyle / RequestFormat / ResponseFormat all in the web.config file. Now, I know I can do this:

  <endpointBehaviors>
    <behavior name="webHttpBehavior">
      <webHttp defaultBodyStyle="Bare" defaultOutgoingResponseFormat="Json" />
    </behavior>
  </endpointBehaviors>

But there doesn't seem to be an attribute for the RequestFormat. How can I set the default RequestFormat to JSON?