@jamie.meyer , I didn't find a way to do this by using the Webex web scheduler (via the web interface of your Webex site).
Would it be an option to use the Cisco Webex Meetings plugin for Outlook (https://appsource.microsoft.com/en-us/product/office/WA104382035)? Once you use Outlook to schedule your meetings, you can put some attendees as optional.
