Provide positive reinforcement when there is no crisis and you'll be able to call on them when there is one. And the corollary is true as well: superstar users, if unappreciated, will leave, and other users will follow them out of your forum.
You can also work some magic in person. Show up to any signings or discussions, even if you just drink coffee and don't participate. Ask for the book at your local library or bookstore. Read the paper version in public (train stations are really great for that sort of thing). And you can also talk to your friends, or email them about the work.