Google Analytics Referral


I have recently signed up to a CPC company and need the refferals to show accuratly after a customer has made payment. However when a customer is Transfered to a payment processor it marks this as the refferal link rather than the origional session as in Google CPC. 

The payment provider web addresses have been added to the refferal exclusion list but this still hasnt worked. Has anyone else had this issue or know of a way to resolve the issue so that google analytics correctly assigns the sale to the correct source,

Thanks in advance for any suggestions here.