PO Link without direct line item mapping

It would be great to be able to link a PO to a bill without having to include specific line items for matching. We do not include certain items in our POs (shipping, handling, rush fees) that are included in secondary bills from our vendors. We are able to match the primary goods POs via the current PO matching process, but we lose the ability to link the secondary bills in our ERP. This means to find these we have to do a lot of searching, rather than just clicking through related records.