I'm with Maytrix on this one. No reason he cannot dive sites where you snorkel for the most part and everyone is happy then. There are a few places like Cooper where you can take the dinghy around Cistern Point and do some deeper dives if desired while the rest of the group hangs out on the boat or the beach club doing their own thing.

Rendezvous diving would be more difficult to control from a timing standpoint. Extra tanks would limit air fills and is pretty cheap for the week so that is a great idea. (4 would be plenty and probably just need one refill spot for the week.

As long as everyone on the boat is reasonable and laid back (a requirement on my boat), then no reason a good time cannot be had by all while accommodating everyone's wants and needs for the trip.

"The Guide to Diving and Snorkeling in the BVI" by Jeff Williams is a great resource for diver and captain to find reasonable locations along your expected itinerary so you can plan better. I used it to plan our upcoming trip where we have 4 out of 12 diving to help avoid a mutinous crew. Lol. Every place where we are doing a dive we have a snorkeling option as well.