Default branch plant on sale order details

Hello,

We have a requierement to have some customer orders with the header branch A in company 1 and some customer orders with the header branch B in company 2. However, the detail branch must be B for all customers. We default the header branch from the ship to business unit, this work well. However, for the customers that have branch A in the header, it is the branch A that default in the detail line and we need to change it every time for B. Is there a preference or a way to have a default detail branch that is