If you pay your employee mileage only, and not an hourly rate, you can run payroll using TaxSlayer Books. Simply log into the account and go to Payroll > Employee Payroll Setup > Select Edit next to the employee you wish to pay > Pay Type: Hourly > Next > Select hourly with 0 as the hourly rate > Add Mileage account under Optional Additions (select the rate per mile) > Advanced > Change pay type to hourly pay. Click Finished >Next > Finish.

When you run payroll, you will enter the miles instead of the hours.