I would like to know if it is possible to only create Po's from a sales order for items we don't have in inventory?

If I create a sales order that has lets say three items two that I can pull from our inventory and one that I don't have any in stock I want to create a PO for only the item that is currently out of stock. I love the generate PO on the sales order as it ties the two together.  But it now would create three PO's and we have to delete two of them. Is there a way to tag the items I don't want to create a PO for?  Would it be possible to create a UDF if such a tag does not currently exist.  

Thanks 

Karen