Need to find a way to tax an employee benefit at the 25% supplemental tax rate

Currently, a group of our employees receive travel supplemental payments that are in addition to their biweekly salary.  We have set these payments up as a benefit in JDE, that is assigned to the employee on their DBA Instruction screen.  I need to find a way to tax these payments at the 25% supplemental tax rate. We do not want to have to manually enter these payments on the employees imported timecard.  Is there a way to set up a pay  or benefit code that will automatically be paid to these employees and taxed at the supplemental tax rate?