For the tenderloin, wrap the tenderloin in the bacon slices. Grill over medium-hot coals, covered with grill lid, for 20 to 30 minutes.
BLUEBERRY SAUCE: Melt the butter in a large skillet over medium heat. Add the onions, salt & pepper. Saute until onions are golden brown, about 10 minutes. Stir in the sugar, and cook for 2 minutes, stirring constantly
Stir in the wine and vinegar, and bring to a boil. Boil gently for 3 minutes. Stir in the blueberries and tomato halves, and cook just until heated through.
To serve, cut the tenderloin into thin slices and place on a serving plate. Spoon the blueberry sauce over the top.