Start by making the blueberry syrup: in a medium sauce pot, combine blueberries, sugar and water and bring to a boil over medium-high heat. Reduce heat to low and let simmer 30 minutes. Remove from heat and let cool slightly before straining through a fine mesh strainer placed over a large liquid measuring cup or bowl; set aside to cool or refrigerate.
To make the lemonade, stir together water, lemon juice, orange blossom water, blueberry syrup and vodka. Pour into glasses filled with ice, about 3/4 of the way high, then top each with club soda to serve.