In a medium saucepan, combine sugar with 2 cups water; bring to a boil over high heat. Add blueberries, wine, and lemon zest; return to a simmer. Cook, stirring, until blueberries begin to burst, about 3 minutes.
Pass mixture through a food mill or a fine sieve into a large bowl, discarding solids. Stir lemon juice into strained liquid. Cover with plastic wrap; refrigerate until completely chilled, about 1 1/2 hours.
Divide soup among six bowls. Swirl about 2 tablespoons buttermilk into each bowl, and serve immediately.