[Callers] When beginners arrive late (Was: Glen Echo FND beginner lesson plan)

In the discussion about lessons for beginners, a few people correctly said that it is often the case that a bus load of beginners will arrive, not a half hour before the dance begins, but instead an hour after the dance has started. It has been my impression that most of the best callers can handle this situation well. They bring the new dancers into the dance, and everyone still has fun doing it. Although the skills of the caller are important, the dance community must also help. How do you, as a caller, handle this, and what does the dance community (the experienced dancers) need to do to make it work?