Anything the customer enters on your site is yours to grab, keep, and store to your choosing. Curl would allow you to keep the customer on your site without leaving at all, are you wanting the information they are posting to Verisign? If so, you would need Curl or something, if not then your problem is easily resolved through your signup form, session variables, whatever. It sounds like your are already able to re-establish state with the returning user.
Perhaps I do not understand the question..