Soften gelatin in cold water in a custard cup. Place in a pan of hot (not boiling) water until melted and ready to use. Combine juices and sugar with melted gelatin. Stir until sugar and gelatin are dissolved. Chill until mixture begins to thicken.
Fold blueberries into mixture. Chill until ready to serve.
Spoon into chilled bouillon cups; garnish with fresh mint.