Light a grill. In a bowl, toss the nectarines with the sugar, cinnamon and 1/2 of the gingersnaps. Spoon 1/4 tablespoon of the butter in the center of each sheet of foil and top with the fruit. Bring 2 sides of the foil up over the fruit and fold to form a seam across the top. Fold the remaining 2 sides to seal the hobo packs completely.
Grill the hobo packs over moderate heat until the fruit is sizzling, about 10 minutes. Open the hobo packs and pour the fruit and juices into bowls. Top with a dollop of yogurt and the remaining 1/4 cup of crushed gingersnaps.