Pour boiling water over the gelatin and stir to dissolve completely. Pour the mixture into ice cube trays with rounded bottoms (you should be able to fill 2 trays). Refrigerate until partially set, about 20 minutes. Push the blueberry eyeballs into the partially set gelatin and refrigerate until thoroughly set. Dip the ice cube tray in warm water for 15 to 30 seconds and run a knife around the edges of each ice cube. Turn the "eyes" out on a serving plate and refrigerate until serving time.