A 49-year-old female with generalized anxiety disorder has had inadequate response to two adequate SSRI trials (sertraline 200 mg for 12 weeks and escitalopram 20 mg for 10 weeks) and one SNRI trial (venlafaxine XR 225 mg for 10 weeks), each producing only partial symptom relief. She continues to experience persistent worry, muscle tension, restlessness, difficulty concentrating, and sleep-onset insomnia. Her GAD-7 score remains 16 despite current venlafaxine XR 225 mg daily. She engages in weekly CBT but reports difficulty applying techniques due to the intensity of her physiological arousal symptoms. She has no substance use history and no comorbid psychiatric diagnoses. Which augmentation strategy is most appropriate?