A 36-year-old male recreational golfer has been complaining of left plantar heel pain for nearly 6 weeks. His pain is worse with weight-bearing, especially the first steps in the morning or after long periods of rest. To date, he has been treating his pain with anti-inflammatory medications and physical therapy. His pain had improved by approximately 40% with these modalities, but the improvements are starting to plateau. What would you recommend next for treatment of his condition?