i haven't been in this particular situation, but people who don't know what to say are all to common. i am not the most sociable guy myself, but i learned to get people talking by asking lots of question, searching for common interests, or simply anything interesting about them. it is a lot of work though, and after such conversations i tend to be exhausted. the irony is that if they didn't want to talk, but get me talking instead, all they would need is to ask a few open questions and then i'd be able to fill the space.