Supposedly, Toastmasters can help with that. I have no idea if you have ever participated in a Toastmasters (and I have not personally) and I realize that once you are a big name, there are challenges to trying to do something like that (I mean it might be a wash because people might treat you differently due to who you are). Just tossing it out there on the off chance that a) you haven't done this b) you didn't know about it for some reason (or hadn't really thought about doing it yourself) and c) you actually have some reason to want to work on this. If you don't do that much public speaking, it may not really matter in the grand scheme of things.
I can vouch for the effectiveness of Toastmasters in addressing the problems the article describes in the first paragraph of "this is Paul Graham". http://www.toastmasters.org/
The rest of the paragraphs in that section are off. I didn't see the presentation, but just reading the writer's complaints about unanswered questions tells me that pg's speech was effective. The goal was to get the audience to want the answers to those questions.
Peace.