At the time of writing, this isn't possible via the fullCalendar API. You would have to re-write fullCalendar's internal rendering code to suit your purpose. It's possible that could be achieved by creating [custom views], but you would need to study the current fullCalendar source code to understand all the possibilities.

Alternatively, you can see if anyone has requested such a feature and vote for it, or submit your own feature request for the developers on the fullCalendar project to consider. Instructions are here: https://fullcalendar.io/requesting-features