Step 1: Prepare the pork chops: Combine the sage, salt, cracked peppercorns, and the 1½ tablespoons of olive oil in a small bowl to make a coarse paste. Using a sharp knife, cut a slit 2 to 2½ inches deep and 3 inches wide into the side of each chop to form a stuffing pocket in the center of the chop. Stuff each pocket with about 2 heaping tablespoons of blue cheese. Rub the sage paste evenly over both sides of the pork chops, place them on a platter, and let stand for about 30 minutes.
Step 2: Set up a charcoal or gas grill and preheat it to medium-high.
Step 3: Make the Concord grape sauce: Heat the 1 tablespoon of olive oil in a large skillet over medium heat. Add the shallots and cook, stirring frequently, until beginning to brown, 8 to 10 minutes. Sprinkle the sugar on top and continue cooking the shallots until they are lightly caramelized, 2 to 3 minutes. Add the grapes, stir to combine them with the shallots, and cook until the grapes begin to release their juices, about 3 minutes. Add the balsamic vinegar and cook for 1 minute. Add the chicken stock or broth and red wine, raise the heat to medium-high, and let come to a boil. Cook until the liquid has reduced by half and the sauce is slightly thickened, 3 to 5 minutes. Keep the grape sauce warm over low heat.
Step 4: When ready to grill, brush the grate with vegetable oil. Place the pork chops on the grate and grill them for 4 minutes, then rotate the chops a quarter turn for nice crosshatched grill marks and grill them for 4 minutes longer. Turn the chops over and repeat the process, grilling the chops until cooked through, 6 to 8 minutes more. An instant-read thermometer inserted into the thickest part of a chop, but not touching a bone, will register between 145° and 150°F.
Step 5: Transfer the chops to the skillet with the grape sauce. Spoon some sauce over each chop and let the chops rest in the sauce for 5 to 7 minutes. Serve the chops with ample sauce spooned on top of and around them.