Place rhubarb in a large saucepan with water to cover. Bring to a boil over medium-high heat, and cook until tender. Drain and mash or puree in a blender.
Stir together the rhubarb puree, sugar, orange juice concentrate, lemonade concentrate, gin and water. Freeze. Place scoops of the frozen mixture into serving glasses, and fill the rest of the glass with lemon-lime soda.