Puree 2 cups chopped honeydew melon in a blender until smooth. Pour into a large cocktail shaker. Add 1/2 cup silver tequila, 3 tablespoons lime juice, 1 tablespoon orange liqueur and 1 teaspoon agave nectar. Rub the rims of 2 rocks glasses with lime wedges and dip in a mix of 1 teaspoon sugar and 1/2 teaspoon coarse salt. Add a handful of ice to the shaker and shake until very cold. Fill the prepared glasses with ice; strain the margaritas into the glasses.