Shipping on buy on advance


I need shiping to charge for an item that i have on buy on advance, so if they buy an item that i have in stock and an item that i have on buy on advance it will charge for bothe with seperat shipping.

At the moment its charging for them both together which means I’m losing out cos i will post the one that is in stock and then post the other one when it becomes available.

So i would like to set up to charge for shipping separately for items that are bought in same order; in stock backordered; and buy in advance.

Any ways of doing this?