Place 3 cups of wild blueberries in a medium saucepan with 1/4 cup water (leave the remaining blueberries in the freezer). Turn the heat to medium low. Stir periodically for 5-10 minutes, until liquid has filled the saucepan and the mixture is just beginning to steam. Remove from the heat.
Pour the juice through a fine mesh strainer into a bowl, gently pressing the blueberries to release as much juice as possible from the skins and pulp. Discard the solids.
Place the bowl in the refrigerator or freezer for several minutes until the juice is cold.
Fill a large pitcher with several handfuls of ice, followed by the seltzer water. Add the wild blueberry juice, lemon juice, and honey, adjusting the flavors to taste. Add the remaining frozen blueberries as well as the mint, if using.