Out of Stock on Orders - How does everyone handle keeping a record/report of what you couldn't fulfil?

How do you keep a record/report of products & Quantity that customers ordered but you were unable to fulfil?

We have used an excel sheet but this can be time consuming. and sometimes no time to be updated between sales

We can't add the product to an invoice with ZERO quantity and add Out Of Stock in the Notes section and then run a report that brings that up.  As DEAR doesnt allow a product to be added if it has ZERO quantity. 

Using BackOrder/ Split Order doesn't work for us as these options create a new Invoice #. Business is against creating new invoices unnecessarily due to business functionality reasons. 

After any suggestions for how other people manage this.

It's helpful so that if target isnt met, we can see if out of stock may have had a bearing on this, if reorder needs to be increased and also who to contact when it is back in stock