On line 309 of the checkout_success page you can add the form values that are stored like:
$clearThese = explode(",","PayPal_ECO_Token,PayPal_ECO_PayerID,eCart_Binder_Items,eCart_Binder_OrderID,WASF_CheckoutWizard_NewFromBlank_Default,eCart_Binder_UPS_Quote");