I don't think any appeal to the actual relativist prof would have been effective. You're talking about persuading someone who not only is much higher-status, and in front of a crowd of witnesses who are liable to jump to your defense if sufficiently provoked, but whose livelihood depends on publicly maintaining the belief system in question. The long-term solution, if it's even possible, would involve appealing to whoever decided to include such classes in the requirements for an engineering degree.