ASP.NET AJAX Synchronous calls

In AjaxPro, if you leave out the Callback parameter, it becomes a
synchronous call.  Is it possible to perform a synchronous call with
ASP.NET AJAX?

Please limit responses to the question posed...let's leave the
discussions of why not async, or what does the "A" mean for another
thread.

Thanks for any help and examples of how to do it.