When you get his address, stamp and address several envelopes, then place them in your pocketbook. Whenever you run into one of his friends give the friend the stamped envelope, a hug and a gentle reminder to write a note.
That is an AWESOME idea! Getting mail from such people always makes the day. I spent a few years running around the planet and when my mail would catch up to me I was surprised by who remembered enough to mail something.