Sounds to me like you're just tempting fate. This comes directly (via copy and paste) from the US Customs website on Customs Information for Non-residents:

"Cigars of Cuban origin are generally prohibited entry, even for personal use. Check with the Customs attaché at the American Embassy if you have any questions on this subject. "

Surely for 8 days you can make do with the inferior non-Cuban cigars. It might make you appreciate your stash back in London a bit more.
Cheers,
Bev