Fill a large pot with 4 cups water, 2 scallions, ginger, and honey; cover and bring to a boil. In a medium bowl, whisk together cornstarch and 1 cup cold water until well combined. Whisk cornstarch mixture into boiling water mixture until it is the consistency of a light gravy. Stir in wine and vinegar; remove sauce from heat.

Add duck to pot and spoon over sauce, for 3 to 5 minutes, until very well coated. Remove from sauce and hang duck again, in a cool room, over a large bowl for 4 hours.

Preheat oven to 300 degrees.

Fill the drip tray of a vertical poultry roaster with water; set in a roasting pan. Place duck on vertical roaster and transfer to oven. Roast until duck is golden and an instant-read thermometer inserted into the thickest part of the thigh (but not touching the bone) reaches 175 degrees. Take care with duck grease as you roast; if too much begins to accumulate in roasting pan, ladle into a disposable heatproof container as the duck cooks and discard.

Meanwhile, prepare frozen steamed rolls according to package directions. Quarter white parts of remaining 5 scallions and cut into 2-inch pieces, reserving green parts for another use.