Nobody gets mileage on the 2106 on the federal return anymore.

You were never allowed to take Mileage to offset the employer contribution. You took the mileage because it was Not reimbursed to you by the employer. Now the only option is to get it paid by the employer under the terms of an accountable plan, or forgo being able to take it as Unreimbursed Expense.

So what should be is that the "employer contribution" should be done under an Accountable Plan, which would make it tax-free to the employee.