Meanwhile, place the reserved wing tips and neck in a medium saucepan, add broth and bring to a boil. Reduce heat and simmer, stirring occasionally, until the broth is reduced by half, 5 to 7 minutes. Strain and discard solids; return the broth to the pan. Squeeze the juice from the reserved orange sections into a small bowl; add cornstarch and whisk until smooth. Stir the juice mixture, reserved zest and brown sugar into the broth; cook over medium heat, stirring, until thickened, 1 to 2 minutes. Stir in the remaining 1 tablespoon soy sauce.