A 68-year-old woman has been diagnosed with a benign ulcer on the greater curvature of her stomach, 5 cm proximal to the antrum. After 3 months of standard medical therapy, she continues to have guaiac positive stool, anemia, and abdominal pain with failure of the ulcer to heal. Biopsies of the gastric ulcer have not identified a malignancy. The next step in management is which of the following?