Discount Amount Control setup option to User

The Discount Amount Control under payment terms on the  Voucher has "Terms " option  always set. We have to change it to User if we want to change the discount to be calculated based on the user date.I am looking to see if we could setup the option for Discount amount control to " User" without the user having to change it manuallyeverytime as our Basis date type is always user entered date.