Combine raspberries and lemon juice in container of an electric blender or food processor; cover and process until smooth, stopping once to scrape down sides. Press berry mixture through a wire-mesh strainer, discarding seeds. Cover and chill.
Cut 1 (18- x 18-inch) sheet of heavy-duty aluminum foil. Place peach halves, cut side up, on foil. Combine brown sugar and cinnamon; spoon evenly into center of each peach half.
Sprinkle peaches with rum flavoring, and dot with margarine. Fold foil over peaches, and loosely seal.
Place grill rack over medium coals (300° to 350° ); place peach bundles on rack, and cook 15 minutes or until peaches are thoroughly heated.
To serve, spoon 2 tablespoons raspberry puree over each peach half.