Well, at the beginning of your speech, I would just be open and tell people you stutter. A little joke you could make after saying this is, "Your patience is not only appreciated, but necessary; trust me, you'll need a lot of it with m-m-me up here." You could also instead say, "With that being said, I hope you're ready for this presentation to take t-twice as long as it should." If you hit a particularly hard block, you could pause and say, "Sorry, I'm buffering" or, "I'm having a malfunction" or maybe "Oops, just had a stroke." At the end of your speech, you could do the Porkie Pig "Th-th-th-that's all, folks!"