Smart Inventory Allocation (Backorder vs Allocated vs Stock on Hand)

We work with distribution companies and small shops, as a result the order sizes for products are any where from a single display pack to multiple master cases. It is common for us to receive an order from someone who may request, for example, 1,000 packs but we only have 50 in stock. Since we do not ship out partial orders, we backorder the 1,000 packs but that results in the 50 we physically have in stock to be allocated to that order. This results in those units not being able to be utilized for another smaller order (or multiple orders). 

If we could manually override or pick what orders we want to allocate that stock to that would be great. Alternatively, if we had an option to manually mark an order as a "Backorder" without using up the stock on hand that would also be great.