Adding a custom attribute to new calendar events through office.js

Question

Is there a way to add a tag or attribute when creating an appointment in AppointmentCompose mode so that it would be available from the graph api later? We have a meeting sync process that uses the graphql api to get calendar events for a given person. We would like to allow the user to mark an item to be synced or not through our office.js add-in for outlook. It would be preferred if the marking mechanism wasn't visible in the email itself when the user is creating it (like not in the subject, body, etc.)