Butterfly lobster tails by using kitchen shears to cut open the shell on the top curved section of the tail. Cut from front to tail, and stop just before the tail. Next, use a sharp knife to slice through 3/4 of the lobster flesh (along the previous cut), taking care not to cut all the way through. Open the tail up like a book. Melt 4 tbsp butter, and mix in 1 tsp salt and 4 oz bourbon. Brush the lobster flesh (not the shell), with the butter-bourbon mixture. Set lobster tails, flesh side down, on the grill. Cover the grill, and cook for 4-5 minutes, or until the shells are bright red and the tails release from the grill plate. Flip tails so that they are shell-side down, and brush the lobster flesh with the butter mixture again. Grill another 4-5 minutes. Drizzle any remaining butter sauce over the tails just before serving.