Need multiple p.o. assigned to a sales orders at different times

As a purchasing agent for our company... When processing a larger complicated sales order requiring multiple supply vendors (or for t.b.d. and quoted custom work) it is sometimes desirable to delay creating ALL purchase orders ALL at one time... pending supply chain issues or just needing to need to change acceptable and willing vendors once the p.o. process is started. While some parts and vendors are standard and can process and ship immediately, some require quotation and lead time for vendor selection decisions. BW only allows one shot at creating this link in sales order p.o. process (conveniently attaching p.o.'s to that sales order at that time). It would be useful not to close out the ordering process and be able to return to continue ordering at a later time.