Moisten the outer rim of a highball glass with 1 lemon wedge and coat lightly with superfine sugar. Add ice to the glass. In a cocktail shaker, muddle the remaining 3 lemon wedges with the Lemon-Thyme Syrup. Add ice and the vodka and shake well. Stir in the club soda. Strain the drink into the prepared highball glass and garnish with the lemon thyme sprig.