Tom,
If you're on Maui, I can't recommend highly enough the crew on the boat called "Desperado" which fishes out of Lahaina - I had a great time with them a couple of years back, got onto some big mahi mahi and had an absolute ball ... no fly fishing with them though, well there wasn't at the time. There's also a guide that runs FF trips out of Lahaina, he advertises in either Salt Water Fly Fishing or Fly Fishing in Salt Water, may be worth a look if you can convince your buddy that it's the best thing since sliced bread. Be sure to post how you get on though - I'll be off there again in a year or two and would love to know how you got on ...
Cheerio,
Shannon