How do you handle a cents per KM car allowance over ATO rate

Hi,

We have some new employees who are on awards I haven't encountered before, that specify a per-km allowance higher than the tax-free rate assigned by the ATO.

Do I need to have two separate pay categories for this? One for the tax free portion (up to 88c per km for 2024-25), and a second category for the extra 10c per km that the award requires and is taxable? 

That's going to be messy on payslips with the allowance showing twice at different rates for the same number of kilometres. 

Is there a better way?

I've seen the instructions for setting up an allowance with a flat rate of tax but that's not quite the same thing.