Heat the sugar and water in a small saucepan over medium high heat until dissolved. Remove from heat and let cool.
[i]Make the pear puree. [/i]
Blend the pears, lemon juice and fresh thyme in a blender or food processor until pureed.
[i]Assemble the drink. [/i]
Fill four high ball or rocks glasses with ice. Shake the bourbon, 2 ounces of pear puree and 1 ounce of simple syrup vigorously until chilled. Pour over ice and top with soda water. Garnish with a sprig of thyme to serve.