I still like the idea of the Bahamas joining the Revolution as its obscure but the population were just sympathetic enough that if they somehow got kept by the Americans in '76 and '78 they would probably stick around.
For that I think you'd need a pretty decisive defeat of the Royal Navy in the Caribbean. That causes a whole different set of butterflies on its own though.
I suppose there's always a chance for a war of opportunity. 1870, during the French Collapse in the Franco Prussian war, the US swoops in and grabs France's Caribbean colonies. Afterwards, it simply writes a cheque to the beleaguered new Republic.
That would be an interesting one.