Any information from the checkout form is available on the confirm page... Unless I'm missing something and your billing information isn't on your checkout page? All of the form information is available on the page specified as the action of the form.
On the DW bindings tab, click the plus button and add the checkout page form references to the confirm page. It will allow you to easily reference all of those values.
Most will also exist in the hidden form that is submitted on the confirm page, so really you could upate when the confirm page is submitted instead.
Did this help? Tips are appreciated...
