Arrange the peaches in a single layer, cut sides down, in a 9-by-13-inch, heavy-duty foil pan. Scatter the butter pieces and sugar between the peaches. Add the vanilla to the pan.
In a small bowl, whisk the lemon curd with enough heavy cream to create a smooth, spoonable sauce.
Place the pan of peaches over direct medium heat and cook, with the lid closed as much as possible, until the peaches are tender, warm and glazed, 8 to 12 minutes (depending on the size and firmness of the peaches), rolling the peaches gently in the butter mixture once. To keep the peaches warm, slide the pan over indirect heat and remove the grill's lid. When ready to serve, slide the hot pan onto a baking sheet and move to a work surface.
Cut the peaches into quarters or smaller slices. Arrange in bowls with the blueberries. Serve warm with the lemon curd spooned over the top.