Each month, choose one referring office and ask whether you may feature their team on your practice's social media
Have your marketing coordinator snap a quick team photo during a drop-by visit, or use one the office sends you
Post a short thank-you that names the practice and one thing their team does especially well, then tag them so they can share it
It costs almost nothing, it gives their practice positive exposure in your community, and it is the kind of thank-you their whole team gets to enjoy.