Depending upon the award Super is generally not payable on leave loading, assuming this is the case you setup a new payrate called leave loading that equals 17.5% of the applicable pay rate. e.g. $20 pay rate = $3.50. When you add it to the employee record you select Tax = Yes and Super = No. This ensures no super is accrued on the leave loading. You then use the pay rate LeaveLoad on payslips where applicable.
To setup a new Pay Rate: Setup Menu -> Payroll -> Payrates
To add to an employee record: Payroll menu -> Employees -> Select Employee -> Options tab
There is no need to add this pay rate to the leave matrix as the underlying payrate will handle the leave.
If super is payable on the leave loading then you can just adjust the standard payrate to increase by 17.5%. e.g. If $20 pay rate then load $23.50.