Hi Steve,
We have a solution that currently does what you are asking for (and more). We de3veloped for a former client that asked for the ability to collate all of their OE order open orders, by customer and by ship to destination (within date ranges), so that they could create a single pick slip (consolidated), and ultimately a single invoice.
The client can pick the pickslips that they wish to consolidate on to a single pickslip, and the pickslip gets generated in OE. They update the picked quantity on the Pick slip and the items are back ordered on the original orders, and the consolidated pickslip is pushed into Adagio OE as an invoice, and printed as an invoice (using Adagio).
Think of it as working the same way as combining PO's into a single receipt. The functionality that you are suggesting is quite common in a lot of sites that have multiple customer orders and they want to minimize their shipping costs, and make the order entry process more efficient.
I know that Softrak is adding to a wishlist but we announced this several years ago, and this does work well.
Best,
Brian