Could you please describe your use-case?
Why would one need to have 2 fulfillment orders in the same location? You are free to fulfill just a part of a fulfillment order with specifying a set of fulfillment order line items.
If I guess correctly, you have products A and B, say product A persists at locations L1 and L2, and product B persists only at the L1 location. They Shopify creates one fulfillment order with both products in the location L1. If I guess correctly, you have constrains/cost optimization leading you to move the product existing in the L2 location to the L2 location anyway?