Displaying substitute material no. instead of original mat. in sales order

Hi,

i have small issue, here when i am creating a sales order i am entering some material number like

'100-100' and quantity as '1' then my sales order asks me for substitute material and there i select one

substitute material number like "p-101" and completing my sales order.

Then when i am checking sales order confirmation form its displaying original material number instead of the substitute material number. i want to display the substitute material number in my smartform.

Try to help me out.

Thanks,

Rajesh