Cancel a Drop Ship Order Line with Approve Purchase Order

Many a time customer has following business requirements.

1.    Customer has Drop Ship Sales Order and that has corresponding Approve PO.
2.    Customer performs multiple receiving, that results in Order line split.
3.    Purchase has still some quantity left for receiving, but customer no more interested in more receiving and they want to cancel the Order line. Let me explain with example
    A.Order Qty = 10
    B.PO Qty = 10 (Approved).
    C.Receiving Qty = 2
        i.Sales Order Line  1.1  - Qty = 2  Status = Closed
        ii.Sales Order Line 1.3  -  Qty = 8 Status = Awaiting receipt
    D.Another Receiving with Qty = 3
        i.Sales Order Line  1.1  - Qty = 2  Status = Closed
        ii.Sales Order Line 1.2  -  Qty =3 Status = Closed
        iii.Sales Order Line1.3  -  Qty =5 Status = Awaiting receipt

Now customer no more interested in receiving qty 5 .Now if he /she try to cancel the line 1.3, system will prompt error message that this line has a Approve PO associated with it.

Solution  - Though this is not full Proof  , but it is good if you have 1 or 2 such cases.
Go to Processing constraints Disable the cancel Line Processing  Constarint associated for “PO Approved”.
Navigate to OM and cancel the line 1.3. cancel process will cancel the line 1.3 as well as update the PO with PO Qty = 2+3 = 5.
Enable the processing constraints.
As I said this is not best solution , but is a good workaround.