Short Close of PO (Drop Ship)

asah

I've read a few posts on how to close out a po that was a qty that will never be received. Can someone tell mme the best way to handle a Drop Ship situation? SO is for 100 units, PO generated for 100 units. Vendor later has only 75 units available but customer decides to receive the 75 and forget the remaining 25 on backorder. We need to invoice the costomer for 75, receive 75 against the PO and close out the remaining 25 on both the SO & PO, how is this best accomplished? Thanks