AP Voucher Discount

Hi,

I am looking for a way to exclude the discount on a single voucher line without the user needing to go into every voucher and manually removing the check box for the discount in the pay terms section.

We include Freight at the line level of the PO and resulting voucher.  We would like to exclude the discount that is automatically applied when the voucher is created without forcing our user to go into each voucher and doing this.  Is there some setup in the Product Item setup that would prevent certain products from being included in the discount on the voucher?