Mix together the salt, black pepper, and sugar. Score the skin on the duck too, but not through, the meat. Rub both sides with the salt mixture, cover and refrigerate 4+ hours, or overnight. Remove from refrigerator and bring to room temperature before cooking (about 1 hour).
Line the wok or skillet with aluminum foil. Mix together the rice, sugar, dried thyme, and peppercorns, if using. Pour into the lined wok. Place the thyme sprigs evenly over the top. Put the rack into the pan.
Pat the duck breasts with paper towels. Heat the wok, when it starts to smoke, place the duck breasts onto the rack, cover with a tight-fitting lid, and smoke for 5 - 7 minutes (for rare).
Meanwhile, heat a non-stick skillet over medium-high heat. Add the oil. Once the breasts have smoked, place them skin side down into the skillet. Cook, until the skin, is crisped, about 2 minutes. Turn and cook 1 minute more. Remove to a cutting board to rest for 5 minutes. Slice thinly on the diagonal and serve.