[jquery] Pass request headers in a jQuery AJAX GET call

I am trying to pass request headers in an AJAX GET using jQuery. In the following block, "data" automatically passes the values in the querystring. Is there a way to pass that data in the request header instead ?

$.ajax({
         url: "http://localhost/PlatformPortal/Buyers/Account/SignIn",
         data: { signature: authHeader },
         type: "GET",
         success: function() { alert('Success!' + authHeader); }
      });

The following didn't work either

$.ajax({
         url: "http://localhost/PlatformPortal/Buyers/Account/SignIn",
         beforeSend: { signature: authHeader },
         async: false,                    
         type: "GET",
                    success: function() { alert('Success!' + authHeader); }
      });

As of jQuery 1.5, there is a headers hash you can pass in as follows:

$.ajax({
    url: "/test",
    headers: {"X-Test-Header": "test-value"}
});

From http://api.jquery.com/jQuery.ajax:

headers (added 1.5): A map of additional header key/value pairs to send along with the request. This setting is set before the beforeSend function is called; therefore, any values in the headers setting can be overwritten from within the beforeSend function.