Just declare the bottle of rum as a bottle of rum (not a bottle of cuban rum) on your customs declaration.
Worst case, it's confiscated - best case, no questions, and continue on your way.
This looks like good advice to me, though I guess it depends how much you value the rum. If you want to be 100% certain it will make it home, you should ship it so it doesn't transit the US. It will end up being an extremely expensive bottle of rum though.