So what if your attendees yawn their way through the keynote. It's not a bad thing, according to this article, Yawning May Boost Brain Power. In fact, it says,
Not only that, brain-cooling explains why you can "catch" a yawn, says Gordon Gallup. "We think contagious yawning is triggered by empathic mechanisms which function to maintain group vigilance." In other words, yawn-catching evolved to help raise the attentiveness of the whole group."
Well, I've learned my new thing for today.