Donate a portion of the proceeds to this group and watch an army of passionate supporters generate sales. Some will buy the book out of support for the foundation. And you will be honored as a hero, generating even more good will and excitement for your program. Many associations depend on vendors to contribute to the event by sponsoring specific items in exchange for additional exposure. Speakers are routinely sponsored, and it wouldn't take much more for those vendors to buy books as well.
Book signings can be great trade show traffic too.
Beyond the event. Don't let the conference itself be the only place where people can buy your book. Many hotel gift shops will gladly display the book during the conference. Just call and ask the store manager and have the books shipped directly to the hotel. Make the same call to area bookstores, especially if your appearance will be publicized through the media.