Rinse ducks inside and out and pat dry. Remove excess fat from cavities and truss ducks. On a metal rack set in a large roasting pan arrange ducks, breast sides up and several inches apart. Let ducks dry, uncovered and chilled, 3 days.
In a small bowl stir together boiling water, honey, and vinegar and cool to room temperature. Brush ducks with some honey mixture, keeping them chilled, and brush again every 20 minutes for 1 hour. Let ducks dry at room temperature 30 minutes. Preheat oven to 350 degrees. Pierce skin of ducks all over with a fork to allow fat to drain and help skin become crisp. Roast ducks in middle of oven until mahogany brown and a meat thermometer inserted in fleshy part of a thigh registers 180 degrees, about 1 hour and 15 minutes. Let ducks stand 10 minutes. Discard string and carefully pour out juices from cavities.
Cut around entire breast of each duck with a sharp paring knife, and carefully peel off crisp skin in large pieces. Cut skin into 2 1/2- by 1-inch strips. Cut away and discard any fat on breast meat and remove breast meat from bone. Slice breast meat diagonally into 1/4-inch-thick slices and arrange on a platter with crisp skin. Remove legs from ducks and arrange on another platter. Duck meat may be reheated and skin re-crisped in a 350 degree oven just until hot.
To assemble pancakes: Using a scallion brush spread some hoisin sauce on a pancake (whole or half) and top with the scallion brush, some breast meat, and some crisp skin. Roll up pancake to enclose filling. Make more pancakes with remaining scallion brushes, hoisin sauce, breast meat, and crisp skin in same manner. Serve duck legs on the side.
Trim roots and green parts from scallions, leaving about 2 1/2 inches of stalk. Fringe ends of scallions by cutting slits about 1/2 inch deep all around both ends of each stalk, leaving about 1 inch of solid scallion in center, and spread fringed ends gently. Put scallions in a bowl of ice and cold water. Chill scallions 2 hours, or until fringed ends have curled.
Drain scallions well.
Mock Mandarin Pancakes:
Preheat oven to 350 degrees. Brush one side of each tortilla with some oil and stack on a large sheet of foil. Wrap tortillas loosely in the foil and heat on middle rack of oven until warm, about 10 minutes. Serve pancakes whole or halved.