Medicare Levy Surcharge additional 1% withholding

Hi Community

Is there a solution for adding a percentage for the additional Medical Levy Surcharge my employee wants me to withhold each week?  My employee has requested:

Claim tax-free threshold   - Yes

Additional withholding amount    -  $0

Medicare levy variation     - 1% Medicare levy surcharge

At the moment I can only enter a $ value and this would work if my employee had the same wage amount week in week out.  I thought I could set up another Tax Payroll Category just for the additional 1% but Accountright doesn't allow me to add another category, only can edit existing standard category.  

There must be a better way than me having to calculate an additional 1% and manually add it to the amount withheld each pay.

Can anyone help?