Using 8 sheets of heavy duty aluminum foil, coat with butter (or use non-stick cooking spray) on one side, just in the center leaving about 2" around the edges.
Using the skewers, place one up-inside each fruit longways (like a corndog) just to the tip of the skewer. Set aside.
In a small bowl, mix brown sugar, lemon juice, and rum. Brush each fruitstick with the mixture. Place onto the sheet of foil.
Stick the bottom end of the skewer through the foil about midway. Fold over the fruit longways and carefully fold or twist the ends to seal, being careful not to tear or make the hole from the skewer bigger (you can pull the foil down a bit and twist around the bottom of the fruit also).
Place on the grill for about 10-15 minutes. Carefully peel back foil, sprinkle (pineapples only) with some salt if desired, and enjoy. enjoy.