deriving business partner / customer number form portal ID

Hi all,

Could anyone offer some advice to a struggling graduate who, for his first assignment, has been thorwn in the CRM deep-end...

I'm developing a 'credit report' portal component which allows business partners to view their credit information for a given date range via a portal. The intention is to emmulate transaction FBL5 on R/3.

The best solution i could come up with invoves essentially calling function module 'BAPI_AR_ACC_GETSTATEMENT' (which compiles the line item info for the statement) on R/3 via a function mudule in CRM.

Theoretically, this setup should work, however it requires a customer number / business partner number in order to invoke the Funcion Module on R/3; which is fair enough... however, the only user information available in the portal (from what i know) is the users login ID.

Is there a standard means of deriving the customer number/business partner number using the portal login ID in either the Portal or CRM?