how to control the qty modification in auto created purchase orders

Hi,

I have a requirement to control the purchase order line qty modification when it created against a requisition through auto create. The buyer should never change the qty in purchase order which is higher than the required qty. I used the profile option PO: Restrict Requisition line modify to quantity split and Requisition encumbrance setup too. It restricts the qty increase while splitting the lines in auto create form. When it creates the PO allows to change the qty.

Any idea would be highly helpful.

Thanks

Shanthi