Planning Workbench - partial fill demand & stock SOP correct?

Our operations manager and I are trying to come up with the best solution for our company regarding the mixed combination of partial inventory in stock and demand for additional parts. In the planning workbench we know how to pull full demand from inventory or make a demand link for the full quantity needed. How do we do a mix and match between stock and production to fulfill a required demand for a part within another job?

My current solution is making a demand link and adjust it for the required amount needed for current active job. Then place a material line into the job on the correct subassembly for the amount we are pulling from stock. We are not setup for ERP. I would love feedback on if this is correct or how we should be completing this process.