In a large saucepan, combine the sugar, flour and mustard. Gradually stir in the pineapple juice, vinegar and soy sauce. Bring to a boil over medium heat; cook and stir for 2 minutes or until thickened. Add sausages; stir to coat. Cook, uncovered, for 5 minutes longer or until heated through. Serve warm. Yield: about 8 dozen.