fly into CUBA, sail out of CUBA

[MoTull]

Hi there,
I originally was going to purchase a one-way plane ticket to Haiti from the US to join a cat as a crew member on their way to Cuba and Guatemala. The details were not lined out, but a crew agreement would have been created beforehand as proof of boat-liveaboard/work situation to present to the Haitian customs. But now my timeline has lapsed a bit, and I am wondering if it is possible to do this through Cuba. Can I buy a one-way plane ticket from the US and present proof of leaving the country on a boat? Perhaps this is an outlandish question and for that I apologize, forgive my ignorance, I'm not sure how to find the answer to this question. I'm thinking I can not buy a one-way ticket and will just have to suck it up and buy a round-trip ticket with one of the 12-reasons checked off for why I am visiting Cuba. Bu then how do I explain leaving on a boat? Any thoughts or advice on this is greatly appreciated.