Passing form data to a success page

My site uses WordPress and contains a contact form built using the WordPress plugin CFormsII. I have a requirement to pass the value of a hidden field to a custom success page. The hidden field contains a unique ID. The unique ID is created from the PHP function microtime. I have already created a variable for the unique ID derived from microtime and created the hidden field with the this variable as the value. When a form is submitted on my site, the data is sent to a third party via the built-in mail function of the CFormsII plugin, the user is then directed to my custom success page. My custom success page contains an iframe to the third-party system which needs to contain the unique ID from the hidden field in the url to ensure the correct data is returned in the iframe to the user. The following page mentions how to pass user data but doesn't go into the exacts: [login to view URL] I require coding to be done to ensure the form data (specifically the hidden field above) is passed to my success page (which is a WordPress page) so that the iframe can use the hidden field value as a variable in the url. Please note: The form submitting data to third party via the mail function must remain in tact. Thank you, Peter.