Step 1Off heat, combine the vodka and simple syrup in a small saucepan. Add the gelatin sheets one at a time to the vodka mixture, breaking up the sheets if necessary so that they can be completely submerged. Allow the gelatin to sit in the vodka mixture until it is soft and pliable, 5 to 10 minutes.
Step 2When the gelatin is soft, heat the saucepan over low heat, stirring, until the gelatin is dissolved and incorporated into the vodka mixture, about 10 minutes. Remove the pan from the heat.
Step 3Check the contents of the pan; if there are any flecks of gelatin that have not dissolved, strain the mixture to remove any solid particles. Place a blueberry in the bottom of each individual cocktail mold, and carefully pour the vodka mixture into each mold. Refrigerate the molds until set, preferably overnight. These cocktails will keep, refrigerated, for as long as 2 days.