A 58-year-old male with severe rheumatoid arthritis presents for elective lumbar spine fusion. Clinical examination reveals limited mouth opening (15 mm), cervical spine rigidity, and a Mallampati score of IV. Awake fiberoptic intubation is planned. After topical anesthesia with 4% lidocaine spray to the oropharynx and 2% viscous lidocaine to the tongue, the patient develops sudden coughing and mild stridor during scope insertion. Which of the following is the most appropriate immediate management?