The Employee needs to have in place an Agreement with the Employer to Salary Sacrifice their Termination Payments. You will need to seek further details from the Australian Taxation Office (ATO) in relation to this matter.
You will need to process the termination as a Manual Calculation, as Deductions Before Tax can't be included in a Termination Transaction.
If part of the Termination is an ETP, then this cannot be salary sacrificed to Superannuation. Seek financial advice first.
Refer here for more information from the ATO: