Bring a large pot of water to a boil. Meanwhile, using a paring knife, score a shallow “x” mark in the bottom of 1 1/2 pounds peaches, just enough to cut the skin. Place 8 ounces of the blueberries (about 1 cup), 1/2 cup granulated sugar, and 2 teaspoons powdered fruit pectin in a small saucepan and stir to combine. Place over medium heat and cook, constantly stirring, until it comes to a boil. Continue boiling, stirring often, until most of the blueberries have burst and the mixture has a jammy consistency, about 5 minutes. Transfer the mixture to a large bowl and set aside to cool.