In a food storage container with a lid, combine gin, lime juice, simple syrup and bitters. Cover and freeze overnight. Pour tonic into an ice cube tray and freeze overnight for tonic ice cubes. Once ready for cocktails, in a blender, add slushy gin mixture, tonic ice cubes, another tray of ice water cubes, and 1 to 2 scoops lime sorbet, then blend until thick and slushy. Divide between 4 glasses, garnish with lime wheels and cucumber slices, and serve with a bar spoon and straw.