Customer master sales office field in billing document

Hi,

When a sale happens, I am required to populate the Customer master Sales office field data  (VBRP-VKBUR) in the corresponding billing document.

When a sales order is created, depending on the sales office from which the sale is made, the Sales office is selected/changed in the sales order. Its this field entry that gets defaulted on to the billing document.

Apart from this, I am required to populate the Customer master- Sales office (VBRP-VBKUR) on the billing document, preferably on the header level.

This should be copied from the Sold to Party sales office.

How can I achieve this?

Thanks,

SS