A 50-year-old man who underwent a restorative total proctocolectomy with an S-pouch 20 years ago for ulcerative colitis presents with a 2-year history of progressively worsening severe difficulty with evacuation, bloating, and a constant feeling of incomplete evacuation. A flexible pouchoscopy reveals a patent pouch-anal anastomosis with a 7-cm angulated efferent limb to a normal-appearing pouch. These findings are confirmed on a contrast pouchogram. Defecography demonstrates normal pelvic floor relaxation with contrast retained in the pouch despite maximum straining. What is the most appropriate treatment option?