How can transport costs be loaded to transfered items without having to assign a sourcing rule per i

 We are implementing IO and we are trying to get the Analysis Workbench to show us transportation costs. Most transportation costs arise from transfers from Distribution Centers to another. So far we have loaded transport costs per Shipping Method per Shipping Network and defined sourcing rules only for the bought items, with the shipping method defined there. Transferred Items where defined at the Organization level in the Inventory module (Source zone, General Planning tab).

What we wish to avoid is to have to assign sourcing rules per every transferred item per organization. How can we avoid this?