Is there any way to manually create a credit order in the Magento backend, without an actual order being attached?

This is the situation: I am making a refund on an order which was done before I started to use Magento. So no corresponding order in my system. 

The accountant needs an credit memo when I refund this. I could create one in the old system or just type one but this would create an inconsistent numbering and layout in my credit memo's (which actually is a small problem, but i was wondering)