Update Z-Field in EKPO with BAPI_PO_CHANGE - Z fields are not created in BAPI's Extension structure

HI Experts ,

Earlier I achieved   to update Z-Field (only one field ) in EKPO table by using  BAPI_PO_CHANGE .

But now my current scenario is bit different from i.e we would like  to add  Z fields in EKPO table by using  BAPI_PO_CHANGE  .

However the  Z FIELD is not created in BAPI's Extension structure BAPI_TE_MEPOITEMX . But directly append in EKPO table .

So would like to know the process to change the update EKPO table .

This scenario we are doing this in BSP . So can any one suggest me any BAPI or FM to achieve .

Note : My client doesn't want to add the Z filed in the EKPO table structure CI_EKPODB .

Regards,

Saravana Kumar S