Prepare the filling: Beat the butter and brown sugar in a mixing bowl with a wooden spoon. Beat in the graham cracker crumbs, lemon zest, cinnamon, nutmeg, cloves, rum and vanilla. Spoon the butter mixture into the pears and loosely place the caps on top. Arrange the pears in the lightly greased aluminum foil pan. (The recipe can be prepared up to this stage several hours ahead.)
Set up the grill for indirect grilling and preheat to medium. If using a gas grill, place the wood chips in the smoker box or in a smoker pouch and preheat on high until you see smoke, then reduce the heat to medium.
When ready to cook, place the pan with the pears in the center of the hot grate, away from the heat. If using a charcoal grill, toss the wood chips on the coals. Cover the grill and smoke-roast the pears until nicely browned and soft on the sides, 40 minutes to 1 hour. Serve immediately.
Variation: You can change the ingredients in the filling, adding ground nuts, candied ginger or other flavorings.