Multiple invoices for one order

I am just looking to see if anyone has ever attempted this. I want to generate 2 invoices based on what is in the cart when the users does the final step in the checkout. The idea is the store has a category of items that are basically pre-order items - so I would identify all those products in the current $order_info and seperate them out and then create a new invoice with a different status code - just curious if anyone has any helpful suggestions/ideas before I start digging?

Thanks in advance all