BKPF Custom Fields update from BAPI

Hello,

I have cutom fields on BKPF table and trying to PARK FI document through "BAPI_ACC_DOCUMENT_POST" by enabling BTE, which is working fine;  but i couldn't get my custom fields value gets populated in BKPF by passing value either in "DocumentHEADER" structure in BAPI or passing from BTE / "DOCUMENT_HEADER" in BTE.

Could someone suggest how we can achieve this.

Thanks

Mani