It would be easier to delete the existing checkout pages and rerun the checkout wizard, on the shipping section leave the option to provide shipping checked, but dont enter any shipping prices.
to do this manually, you would need to add each of the shipping info form elements to the checkout page, then on the confirm page, in the collection of hidden form elements, add new hidden form elements to mirror the ones added to the checkout page, and add a set session value behavior for each of the shipping form elements from the checkout page.