cost to include marketing expense

our objective is using unit costing to include marketing expense by product as well as BOM&routing, because in CK11N, we can only get cost from BOM and routing.

so do we need to set up sales BOM? if we don't use sales BOM, what's the T-code to run sales unit cost estimate? can it be done at material/plant level instead of sales order level?

any best practice document in content library for sales unit cost estimate? thanks