Only American boats are prohibited from sailing to Cuba from the
USA. Other nationalities, like Canadians are allowed so you may be able to hitch a ride from one of them.
I know this to be true because I sailed from Marathon to Varadero Cuba two years ago and I faxed the USCG before I went and asked if there was any
permit needed and they faxed me back:
" A
permit is not required. have a safe trip".
Paul