Instead of just having one lumped SUM for a days CPO, users would have the option to add individual orders. Here's how it would work. When a day's CPO cell is selected a small box would open up kitty corner to the cell. This little box would have multiple inputs holding orders that the user has entered.
They key to implementation on this is speed! It has to be quick! Features regardless of functionality, can be very tedious to use if they aren't super easy to use.