Welcome to the Community, @AJMar.
I can understand how convenient it would be to have the ability to transfer funds directly from QBO Payroll to a Vanguard SIMPLE IRA. However, this option isn't available in QBO Payroll.
With that being said, you'll need to process your retirement contribution outside QuickBooks. You can also look for a third-party application to help you with the process.
You can find additional details on retirement plans in the following articles:
You may want to e-pay and e-file your taxes with QuickBooks. Here's an article with details on how: Pay and file payroll taxes and forms electronically in QuickBooks Online Payroll.
I'm here to assist you with anything you need or if you have any further questions about your retirement plans. Feel free to reach out again. Take care.