It will be obvious when the interview is drawing to a close. You will receive an offer. You will be rejected based on this interview. Ask when you will be notified.
Interviewers like to hear positive things, too.
If the chemistry is good between you, he needs to know it so he will put in a good word for you. Summarize what you can do to solve what you perceive to be the employer's greatest problem. Employers though, almost always resent an approach which places them on the spot. Do not resell your qualifications or list why you are perfect for the job. Short and to the point, thank the interviewer, express your enthusiasm and commit to pursuing the opportunity further.