Methyl Mike:
Tell your buddy to perform a "sweat test" run. Weigh himself naked, go run for an hour, come home and weigh in naked again. The weight loss is water. That will tell him how much he needs to take in per hour to hydrate during the race. Try to keep factors like paceN clothes and weather similar to expected race conditions during the sweat test. He will need to plan on not taking in more than 6 ounces of water at one time, or it will slosh around in his stomach.
If Gu bothers him, have him buy high carb jelly beans at a running store - easier to take in small amounts. Forget the carb bar suggestion.
You mention he's done "some long runs". He should understand that a good goal for a first marathon is just to finish. Under 3:10 and qualify for Boston is a lofty goal. Not trying to talk him out of going for it, but 3:10 is moving at a good clip.
Tell him to be careful with the water intake. It's probably the second biggest mistake new runners make. Too much can kill him also, so it can't just be a wild guess.