"Project Stock (components" for subcontracting process

Dear SAP Gurus, our customer faces the following challenge: We have a subcontracting process in place. We create a purchase order for the final product at the subcontractor. The purchase order is linked to a WBS element. As we need certain components for this process, we purchase them from a supplier. Once goods receipt for the components is posted, we deliver those components to the subcontractor (goods issue via app “Subcontracting Cockpit”). Once the final product is produced, the subcontractor delivers it and we post the goods receipt. The requirement of our customer is, that all components which are delivered to the subcontractor should be linked to a WBS element (same as from PO). As some subcontracting processes last over a long time period, our customer must be able to identify the stock (of components) which is used in which project. This is necessary for reporting purposes, e.g. for manually calculating WIP for projects. Our problem is that we can’t assign the purchase order of the components to an WBS element, as in this case the goods receipt of the components would be posted to consumption. In this case we can’t deliver them to the subcontractor, as they are not in stock. In case we don’t assign the PO of the components to a WBS element, it will be posted to stock, but we don’t have those components linked to the WBS element and hence the requirements of the customer can’t be met. Does anyone of you have an idea on how to solve this challenge? Thanks and best regards Christoph