A 68-year-old man with advanced gastric cancer presents to the emergency department with intractable vomiting for 6 hours. He has a history of gastric outlet obstruction and is currently on metoclopramide 10 mg TDS. On examination, he is dehydrated and has visible peristaltic waves. Abdominal imaging confirms gastric outlet obstruction with no acute perforation. What is the most appropriate next step in management?