How to populate field XBLNR_ALT in table BKPF through BAPI_ACC_DOCUMENT_POST

I have a requirement to populate BKPF-XBLNR_ALT field through my program which is using BAPI_ACC_DOCUMENT_POST to create accounting document. But the header structure 'DOCUMENTHEADER' has no field which can be used for this purpose. How can i solve this problem?

Regards,

Meenu