Treatement of normal and FOC item in inventory

Dear Experts,

We have a requirement in which same material has to be in stock with value and as FOC item also. (We don't want averaging of price)

Business Scenario: Stock of item A is 100 QTY with value 1000 $. Vendor provides as special stock (For demo/display purpose) of the same item with 0 value. Both the stock exist in our inventory, i.e 100 qty with 1000 $ and 10 qty at 0 price. After the promotion period we need to transfer this stock to normal stock with normal stock value.

How we can achieve this. Kindly help.

Thanks & Regards

Ranjit Simon