Brad, how about partnering with your business to business relationship for a coupon or the like that you can send to them. Could be something as simple as coffee, or regular maintenance on their home, chimney cleaning, termite inspection, etc.
How about updated home price analysis? Depending on how long they have been in their homes.....They might come to find out they have more equity, and list with you again.
I like your question, I am interested to see if anyone else shares some ideas.