It's not possible, dave. I understand the need to set up pension salary sacrifice in QuickBooks Online (QBO) Payroll Core. However, this feature is limited to Advanced payroll. Let me share more details below.
You can only set up regular pensions or workplace pensions in Payroll Core. While enabling salary sacrifice pension in Payroll Core is unavailable, consider upgrading to QBO Payroll Advanced.
If you've upgraded your payroll subscription, you can visit this link for future guidance in setting up a salary sacrifice pension and managing advanced payroll:
Always remember that I'm here to help with salary sacrifice setups and other payroll queries, dave. Feel free to post your questions below and I'll gladly assist.