Robin,
If you have another friend who is a good pilot that believes in taking proficiency training, or if you know someone who is an instructor pilot, try getting the three (or more) of you together for lunch somewhere or at a Pub, where the topic will naturally flow to flying. Bring up the topic of proficiency training and as a non pilot start asking questions that you think are pertinent about training and flying (pursue it on the premise that you are interested in learning how to become a safe and knowledgeable pilot. With luck your friend will realize that it would not be a bad idea if he took some proficiency lessons from a certified instructor.
If this doesn't work, even though I throughly love to fly, I would politely decline to go flying with your friend.
Think about this way, the life you save may be your own, or it is far better to read about statistics than to become one.
Mike