Arrange pear halves, cut side up, in an ungreased 13" x 9" baking dish. Stir together ginger ale and next 3 ingredients. Pour ginger ale mixture over pears; sprinkle with 1/4 teaspoon cinnamon. Cover and chill at least 3 hours or overnight.
Remove pears from refrigerator, and let stand at room temperature 30 minutes. Uncover and bake at 350° for 40 minutes.
Melt jelly in a small saucepan over low heat; stir in remaining 1/4 teaspoon cinnamon and 3 tablespoons pan juices.
Remove pears from baking dish using a slotted spoon. Place pears in a serving dish; pour jelly mixture over pears. Serve with Mock Devonshire Cream. Garnish, if desired.