I need some Ubercart Backorder advice

We have an eCommerce site using Ubercart. Currently when an item is out of stock we do not let the user order any more. I would like to enable orders to be placed for items that our out of stock and have a way for us to be automatically notified when more stock comes in related to those orders. Alternatively maybe those orders go into a queue, and aren't really "placed" until there is stock available at shich point they become an active order.

I just think that back-orders are a common enough thing that someone must have developed some sort of system already.

I am not opposed to paying to have a module developed or expanded, but I would appreciate some advice on the best way to handle this type of scenario.