I don't have an exact answer to your question but here is what I know - there is a small airport in Cayo Santa Maria and they do have charter flights going to Havana for hotel guests wishing to visit the city. Now would it be possible to arrange a transport on one of these charters - who knows. But, if my little travel experience is any good, they will be always open to accomodate you if you have some pesos that you're willing to part with.