I think you may be able to book passage on a cargo ship.
go to
http://www.jocsailings.com/
Enter origin as Djibouti, destination as Salalah, date range as 120 days.
You will get a substantial listing of ships that are making that route.
There are 2 main carriers. One, explicitly offers tourist bookings. See:
http://www.cma-cgm.com/ProductsServices/Cargo-Cruises/