Just a little experience from an interview I sat yesterday.
I was being interviewed by the IT Operations Director and the Customer Services Director as my role previously was a hybrid of both areas.
Clearly two separate area's with each interviewer asing question specific to their section, and boring to the other party.
I found myself focussing on the person asking me the question and decided that I needed to bring the other person into the discussion. If not verbally then definately gesturing to them, eye contact etc. including them really.
What I discovered is that the Client Service guy was doodling and when he realised that I was actively including him, he stopped, sat up and started (well looked like) he was listening.
Really what I'm saying here is try and include everyone interviewing you.