To prepare the pineapple, pull off the green top by "unscrewing" it. Reserve the best leaves for decoration by placing them in cold water, trimming them if needed to make their shape a little more perfect.
With a large sharp knife, cut the peel off the pineapple and halve it lengthwise. Reserve half the pineapple for another use. Cut the remaining pineapple in half lengthwise and cut out the core. Cut the pineapple into 1 1/2-inch thick slices and then into chunks.
In a bowl, whisk together the syrup and rum, if using. Toss the chunks in the maple syrup and thread them, alternating with blueberries, onto the wooden skewers. Lay the skewers in a shallow dish. Pour the remaining syrup over skewers. Cover and chill. (The skewers can be assembled up to a day in advance.)
To grill skewers: Brush the fruit 1 more time with maple syrup from the bottom of the dish. Fire up your grill and place the skewers on to cook them, turning occasionally, until caramelized.
To serve: Place scoops of vanilla ice cream in dessert bowls, arranging 2 pineapple leaves at the back like rabbit ears, then place a skewer across each bowl. Pour any remaining maple syrup over the ice cream and serve immediately.