I suspect you are looking at it wrong. Most people think the person interviewing them is hoping to find something to judge them on and disqualify them. But if you think about what they are really doing is a job. It may even be a job they don't want to do. They want to get it right and they likely want to get it over with. So, if they are any good, they are going to be disappointed if you don't fufill their qualifications. Usually, they want you to be the right candidate and hope against hope that you are.
You are better off thinking of the person you are interviewing with as an advocate within the company to get your hired. This person is your best friend who is bugging the boss to get you a job. In order to make that relationship work you have to become at ease with this person. The sooner you do that the easier time you will have. Because you do have to convince them you deserve a shot.
I think the best technique for doing this is talk to the interviewer like they were already a friend. Ask them a question a soon as you can, phrase it first to be about the company and then turn that so you are talking about them. You want to get them to tell you both about the company, about their relationship with and within the company, and the position. Getting them to do most of the talking initially and it will put you both at ease (by the way interviewing people isn't necessarily easy either).
One job I ended up with happened because I impressed the interviewer with a different company. He needed a more experienced person but the company he previously worked for needed someone at my level. I hired on there and eventually started a business with the interviewer. My point is...the guy didn't think I was qualified for the job he had but he wanted to help me find a job. I think most people are that way...I really do.