I think you misunderstand how the Payments pro process works.
On the checkout page, there are 2 options the user can chose for payment:
1) Direct payment - this is when they fill in the checkout form on the checkout page
2) Express Checkout through Paypal - This is when they click the paypal express checkout button on the checkout page.
each payment method has a different set of pages.
Using Direct payment, the user fills in the checkpout form, and this is posted to the confirm page. on the confirm page, the user confirms the purchase and it is processed through payla.
You have the special instructions as part of the checkout form, so setting the session and the hidden element must happen on the confirm page.
using the express checkout option, the user goes to paypal to set the payment method, they atre then returned to the pp_confrim page. here they can confirm the order and process it through paypal.
