A 42-year-old man with a 3-year history of episodic severe headaches, palpitations, and profuse diaphoresis is found to have sustained hypertension (160/95 mmHg). Imaging reveals an encapsulated tan-brown adrenal mass (marked **A** in the diagram) measuring 4.5 cm with central hemorrhage. Biochemical testing confirms elevated plasma free metanephrines (3.2× upper limit of normal). The structure marked **A** in the diagram is a catecholamine-secreting tumor arising from chromaffin cells of the adrenal medulla. Prior to surgical resection, which of the following pharmacologic approaches is most appropriate for pre-operative management?