It can’t really be achieved as long as you want to use the outside operation concept. At least not without creating these documents as configurations/modifications.
To have the full shipment functionality available you would need to add the part you ship as an inventory purchase part with a purchase structure and use purchase order instead of a shop order with outside operation.
Please consider creating a request in the Idea section of the community to be able to use the shipment functionality available in IFS also for shipment of WIP for outside operations. I believe it would be valuable for many companies.