Hi Ralph,
One way to achieve this since your in the SRM classic model, is to create your cart for material item in SRM. This would transfer to ECC as a reservation for your part - stock. You issue against the reservation. MRP runs daily and generates a requisition-then a PO in ECC to replenish this part using the source list either fixed vendor or outline agreements (this is standard ECC functionality).
hope it helps,
Daniel