Soak 8-inch wooden skewers in warm water for at least 45 minutes before using. In a small bowl combine soy sauce, vinegar, ginger, garlic, oils, brown sugar, cayenne and 1/4 cup water. Thread vegetables on skewers and place in a shallow glass baking dish. Pour soy sauce mixture over and marinate skewers, turning several times, for at least 1 hour at room temperature. Preheat grill. Place skewers on grill and cook, turning and basting frequently with extra marinade, for about 6 minutes in all.