I haven't used blueberry but I have used other fruits and done a lot of research on this. I think I would use fresh blueberries, pasteurize, and puree. I would put those in the secondary. I would also consider using some three olives blueberry vodka to sanitize the blueberries and then add the vodka and blueberries together.
Anyways, the next important step would be at bottling. That's when you would want to add a little blueberry extract to really get the blueberry aroma.
You could also consider adding spices to the secondary, like vanilla beans, to accentuate the blueberry flavor.
On hand or fermenting
Oud Bruin /vanilla
Pre prohibition Cream Ale
Mexican Stout in BB