Take a sip or two from the Carib. Replace the volume with Bacardi Limon. Cover the top of the Carib bottle with your thumb or the palm of your hand and invert the bottle for about 15 seconds to allow the rum to mix into the beer. Do not shake!
If you cannot get Carib lager, you might try substituting Negra Modelo or Dos Equis Lager. As a last resort, you might also use Corona.
Our thanks to Mike Kneafsey for this one!