[patio11]

This is about as close to a pure speech hack as I'm aware of, by the way. It makes you immediately, perceptibly better, and even if I told you "Here's a video of me talking. Hit a buzzer when I'm buffering" you'd miss most of them because they read as dramatic emphasis to the audience. (The umms, stammers, and verbal disfluencies, on the other hand, are instantly perceptible.)

As long as we're on the subject of hacks: pick three people in the audience: one on the left, one in the right, and one a bit off center in the middle. Always make eye contact with them when you are speaking. Rotate every couple of sentences. BAM, perceived confidence goes way up.