Soak wooden skewer in water for 20 minutes before grilling. Meanwhile, oil grill and prehet to medium-low.
Stir yogurt with maple syrup, orange peel and vanilla.
Peel kiwi and cut into large bit-size chunks. Peel pear, if you wish, or leave skin intact. Then cut pear and nectarine into 1-inch wedges. Thread fruit randomly with cake, if using on skewers.
In a small bowl, stir butter with sugar and cinnamon.
Place skewers on grill and barbecue, turning frequently, until fruit is hot and cake is grilled, about 4 minutes. Just before removing from grill, brush fruit with butter mixture. Serve with dipping sauce.