Customer no to populate the Assignment field for Sales A/c using sort key

Dear All,

In 6.0, I am trying to get the Customer number to populate the Assignment field for Sales Account

We have set the sales account to a 031 sort key - sort by customer, in FS00. When 031 is set, SAP goes to the BSEG table and looks at the KUNNR (customer) field and populates the Assignment field with what is in the KUNNR field of BSEG.

The problem is: the customer number (KUNNR) does not contain any data in BSEG.

The KUNNR field of all the other account lines for the document number are blank.

Is it possible to bring the field in the General Ledger display?

Does anyone know of a user exit or other solution?

Thanks,

Gov