Combine syrup and butter; set aside. Quarter the pineapple lengthwise, leaving top attached.
Moisten a paper towel with cooking oil; using long-handled tongs, rub on grill rack to coat lightly. Grill, uncovered, over medium heat for 5 minutes. Turn; brush with maple butter. Grill 5-7 minutes longer or until heated through; brush with maple butter and sprinkle with nuts. Serve with remaining maple butter.