Problem using Wizard control and synchronous SOAP request

Question

I have a multi-step Wizard control in a content/master page that holds many form elements. On the Finish step I wanted to build a SOAP request from the element values and send it on the onLoad of the Complete step. This does not work because all steps are loaded on each post back and the client sits and spins until the XML comes back and the page finally renders. I tried using cross page posting to post all the elements to a different page, but still the page waits for the SOAP response before rendering the page to the browser. Using post-back I lose the PreviousPage reference. How can I render the page then send the request to avoid the user waiting 1.5 minutes before they hit the confirmation page?