A 52-year-old man with a 10-year history of bilateral lower limb varicose veins presents with recurrent episodes of superficial thrombophlebitis. On examination, he has extensive GSV varicosities with a palpable cord in the medial thigh and mild ankle edema. Duplex ultrasound confirms GSV incompetence with reflux >1 second, patent deep venous system, and no evidence of deep vein thrombosis. He is keen to avoid surgery. Which of the following is the MOST appropriate next step in management?