Preheat broiler. Melt 3 tablespoons butter in a medium saucepan over medium heat. Stir in shallots, and cook 20 seconds. Add wine, and simmer until it has been reduced to 1/2 cup, about 10 minutes. Add scallops; cover, and cook 1 minute. Using a slotted spoon, transfer scallops to a cutting board. Pour poaching liquid though a sieve into a bowl.
Cut each scallop crosswise into 2 or 3 slices, cutting almost but not completely through. Fan open, and divide among shells. Transfer to a rimmed baking sheet, and spoon 1 tablespoon poaching liquid over each shell. Sprinkle with salt, and dot with remaining tablespoon butter. Broil until just bubbling, 1 to 2 minutes. Sprinkle with peppercorns, and serve with lemon wedges.