In a blender mix together the rum, lime juice, frozen pineapple and ice cubes. Blend until well mixed and smooth. Taste. Want it sweeter, add a teaspoon of lemon or lime sorbet and buzz again, quickly. Pour the contents into a martini or short glass, leaving room on top for a healthy splash of ginger beer. Garnish with a chunk of pineapple or a lime slice. Enjoy!