How do I not charge for unfulfilled products?

[prestigesalonse]

Is there a way to not charge for unfulfilled products on an order? We occasionally will have orders come in and we are unable to fulfill all of the items. All I want to do is not charge the customer for items that are unfulfilled on an order. But I can't see how I can't adjust the total due for an invoice. This seems like a simple thing but apparently it's not. 

Any help?