Yes, I believe that would be fairly easy. I don't know Fire Island, but can see a yacht club at Saltaire, which may or may not accept transient docking. From there, it's a straight run under the Robert Moses Causeway bridge to the vacant lot in Oak Beach on the bay side with the path leading directly to JB's house. I picked that spot on FI to depart because it's roughly 5miles, which in a "No Wake" zone would mean speed limit of 5mph = one hour. If yoiu can get outside the "No Wake Zone" into a channel, you could probably do it in 15 minutes. However, please note that there's a minor issue when you arrive of no dock to moor the boat , although easy to tie up to one of the neighbor's docks either side. For that, you'd need permission from the owner, but it's neighborly thing to do and out of season, I'm sure nobody would have a problem with it.
To confirm (or refute) all the above, you'd want to check with someone who has actually navigated those waters (I have not), or at least look at the charts for 5 mph zone, minimum 4ft depth of water at mean low tide on the neighbors dock, and you'd want to check the tides and weather for that particular date. This would determine what kind of boat you could get in and how long it would take.
Sorry, I don't have time to do all that homework, but will do it if it ever points in that direction and in the meantime, hope this answers your question.
8 the fairway, oak beach, ny - Google Maps
ETA: I'm now thinking it's entirely possible that John #2 arrived at JB's by boat from Fire island, although engine noise amplifies at night, and boats have lights which are visible from occupied homes on the shore.
