To the best of my knowledge Saba now runs the Saba Express, leaving Loose Mongoose every day at noon. I would assume this is for overnight guests but don't know if they make exceptions. At the least I would think they would want you to make a dining reservation.
This of course would put you on Saba and then you would take the water taxi back to mainland. Can't hurt to call Saba and inquire. It would be awesome if they agreed to take you.
If that doesn't work, there really is no other way to avoid either Spanishtown or a water taxi.
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