Grill pineapple slices over medium heat 6 to 8 minutes or until lightly charred, turning occasionally. Cut 2 of the slices into wedges. Set aside. Coarsely chop remaining pineapple.
Place chopped pineapple, coconut milk, pineapple juice, rum and sugar in blender container; cover. Blend on high speed until smooth. Add ice; blend until slushy. Pour into beverage glasses. Garnish with grilled pineapple wedges.