Make the ginger syrup: In a small saucepan, combine the fresh ginger, agave, and water. Bring to a boil then reduce to a simmer and cook for 35 minutes. Careful not to cook at too high of a temperature or the ginger will burn. Set aside to cool.Make the margaritas: In a cocktail shaker (or a large jar) muddle the blueberries and lime juice until the blueberries are pulverized. Add the tequila, ginger syrup, orange liqueur and a handful of ice. Shake vigorously for 15 seconds. Add ice to two glasses then (using the cocktail shaker or a fine mesh sieve) strain the liquid into the glass. Garnish with lime and blueberries, serve and enjoy!