在Windows Phone 8中如何共享图片而不将其保存到图库?

我正在使用ShareMediaTask共享图像。我能够做到这一点后，保存图像到我的手机画廊，但我想要它保存到画廊之前直接。我该怎么做呢?我已经这样做了，但是我不想在分享之前打开照片选择器任务，我想直接分享。

    private void mnuShare_Click(object sender, EventArgs e)
    {
         using (MemoryStream stream = new MemoryStream())
        {
            WriteableBitmap bitmap = new WriteableBitmap(LayoutRoot, null);
            bitmap.SaveJpeg(stream, bitmap.PixelWidth, bitmap.PixelHeight, 0, 100);
            stream.Seek(0, SeekOrigin.Begin);
            using (MediaLibrary mediaLibrary = new MediaLibrary())
                mediaLibrary.SavePicture("Picture.jpg", stream);
        }
       MessageBox.Show("Picture Saved...");
        var chooser = new Microsoft.Phone.Tasks.PhotoChooserTask();
        chooser.Completed += chooser_Completed;
       chooser.Show();
      _fileName = e.ToString();
    }
    void ShowShareMediaTask(string path)
    {
        ShareMediaTask shareMediaTask = new ShareMediaTask();
        shareMediaTask.FilePath = path;
        shareMediaTask.Show();
    }
    void chooser_Completed(object sender, PhotoResult e)
    {
        _fileName = e.OriginalFileName.ToString();
        if (e.TaskResult == TaskResult.OK)
        {
            ShareMediaTask shareMediaTask = new ShareMediaTask();
            shareMediaTask.FilePath = _fileName;
            shareMediaTask.Show();
        }