Bring the sugar and 2 cups water to a boil in a medium saucepan over high heat, and cook until the sugar is dissolved. Remove from the heat, and stir in the basil, mint, tarragon and orange peel. Let cool to room temperature, then cover and refrigerate until cold, at least 4 hours and up to 24 hours.
Strain the syrup into a pitcher, discarding the solids.
Fill six tall glasses with crushed ice. Add a few tablespoons of the syrup to each, then stir in 2 tablespoons of the orange juice and a shot of vodka. Top off with club soda, and garnish with an orange twist and a mint sprig. Serve the remaining syrup to sweeten as desired; leftover syrup can be stored in the refrigerator for up to 2 weeks.