A 68-year-old male with COPD and severe kyphosis presents for emergency repair of a perforated peptic ulcer. Rapid sequence intubation is planned. After loss of consciousness with etomidate and rocuronium, the anesthesiologist notes that the patient's head cannot be extended due to severe thoracic kyphosis. Manual ventilation with 100% O₂ is difficult, and the SpO₂ drops to 88% within 60 seconds of apnea. On direct laryngoscopy, only the epiglottis is visible (Cormack-Lehane Grade 4). What is the most appropriate immediate action?