Packing Slip - 1 Item in multiple Boxes

We have a product which we need to ship in two boxes as one of the component is fragile. We need to generate packing slips for both.
In packing slip when I put packages from 1 to 2 it gives an error saying that “Quantity for Item Test1 must be less than 0.5”. There should be an option which gives 2 packing slips Item Test1 1/2 and Item Test1 2/2.
Can someone guide me how can we make these packing slips?