I saw this recipe earlier at:
http://www.wikihow.com/Make-Blueberry-Soda
Alton Brown's recipe is here:
http://www.foodnetwork.com/recipes/alton-brown/blueberry-soda-recipe/index.html
It seems like a few more steps, but I think they're helpful.
In the end they both come down to adding carbonated water to the syrup.
You could always figure out your volume of syrup and water needed to bring the batch to full strength then bottle in 2 liter bottles.
But I'm more inclined to recommend you keep it as a syrup and add the carbonated water.