How can you value Inventory using the exchange rate at the date of receipt?

We are currently on R12.2.5, and use average costing for our Inventory costs.  We currently use the exchange rate value as at the date of the PO to value our Inventory, but this can mean that there are significant exchange rate losses due to the length of time between the PO being placed and items being received against the PO. 

We would like to know if it is possible to value the inventory receipts using the exchange rate in effect at the date of the receipt, rather than at the date of the PO?  How could this be achieved?

Many thanks,