Bring three-quarters of the champagne to a boil in a saucepan. Remove from heat and let cool. Combine the sugar and water in a pan and stir to dissolve sugar. Bring mixture to a boil, and let cook 20 minutes, stirring frequently, until syrup forms a thread when pulled between your thumb and forefinger. Remove from heat immediately. Stir champagne and fruit juices into the sugar syrup; cool. Freeze mixture in a plastic container until hard, several hours or overnight. In the bowl of an electric mixer, beat sorbet until smooth. Return sorbet to freezer until firm. Serve scoops of sorbet on chilled plates or in glasses, garnished with wild strawberries or strawberry slices. Adapted by Karen Mintzias, from a recipe by Rose Elliot in: "The Complete Vegetarian Cuisine"