Whisk together the soy sauce, vinegar, oils, ginger, garlic and sugar in a small saucepan. Bring the mixture to a simmer over low heat and cook for 5 minutes. Set aside to cool.
Bring the chicken broth to a boil in a heavy saucepan. Add the couscous, remove from heat and cover. Let stand for 10 minutes. Fluff couscous with a fork and let cool to room temperature. Just prior to serving, toss the couscous with desired amount of vinaigrette. 4 servings.