Preheat oven to 350°F. Place potatoes in a small bowl or directly a rimmed baking sheet, and drizzle with oil. Sprinkle with 1 teaspoon of the salt; toss to coat.
Spread potatoes in a single layer on the baking sheet, and bake about 40 minutes, or until tender when pierced with a toothpick. Remove from oven, and cool 10 minutes.
Cut each potato in half crosswise. Carefully scoop out potato pulp leaving the skins intact. Place pulp in a medium-size bowl.
Place shells, cut side up, back on the baking sheet, and bake another 10 more minutes. Cool completely.
Stir together potato pulp, mayonnaise, sour cream, mustard, chives, dill, capers, pepper, and remaining 1/2 teaspoon salt.
Carefully spoon the filling mixture into each potato skin.