Combine sugar with 1/3 cup water in a small saucepan and set over medium-high. Bring to a boil, stirring occasionally, until sugar is dissolved. Stir in thyme sprigs, lemon peel and peppercorns. Remove from heat and let stand 25 min. Strain syrup through a fine sieve, discarding thyme, lemon peel and peppercorns. Refrigerate until chilled, about 10 min. Fill each of 4 glasses with 1/2 cup wine and 2 tbsp thyme syrup. Top with sparkling water. Garnish with a thin half-moon slice of lemon skewered with a small sprig of thyme.