BADI or FM : To Maintain billing Due List from service Order

Hi Experts,

I have requirement for copy data in item to custom added field to Bill Due List.

I have custom added field branch code in Service order Item ,

Now i want to copy that field value to Bill Due List Table .

I added that same field to Bill Due List Also.

Please suggest me any FM or BADI to maintain that field in Bill Due List.

In advance Thanks.

Regards

Alok