I do not recommend substituting with fresh blueberries because this will drastically change the moisture level of your bars and they won't be as firm. You can make your own dried blueberries at home. Simply wash and thoroughly pat dry your fresh blueberries and spread evenly on a parchment lined baking sheet. Let the blueberries dry in the oven for 8 to 12 hours at 140F , or until they are shriveled, slightly leathery, and have a chewy texture.