Well, random ideas:
Red Hook Dive Center in Red Hook is my "home" scuba center.
St John is great. Not sure what he likes to do. You can go for an afternoon and evening and have a great time. Hike to Salomon Beach, beer at the Tap Room, wander and see what looks interesting for dinner.
Morning Star is a great beach, although it is usually windward, can have some waves. There is a very nice beach store there, Coco Joe's. <img src="http://www.traveltalkonline.com/forums/images/graemlins/Wink.gif" alt="" /> What does he like to do with his beach time?
I'm pretty sure there are day sails booked out of the Adventure Center at the Reef. Might go to Buck Island,which actually has some nice snorkeling.
Downtown Charlotte Amalie pretty much closes at 5. Close to the Reef is Yacht Haven Grande- several bars/restaurants, shops, too. Mega yachts to drool over, too.
I agree that Frenchtown is a great place to dine- Bella Blu, Hook, Line, and Sinker, the Pie Whole, etc. If he goes to St John, he can stop in Red Hook on the way back- ITP, Fish Tails, XO...Lots and lots of ideas. <img src="http://www.traveltalkonline.com/forums/images/graemlins/Grin.gif" alt="" />