如何在设计视图中为自定义控件添加边框

透明图像在Windows窗体中是纯粹的邪恶，这就是为什么我创建了一个自定义控件类来处理它们。当我的控件为空时，设计器不会显示它。我想添加一个微妙的边框，但只能在设计视图中添加（当用户没有添加边框时）。我该怎么做？

我的课是：

class TransparentImage : Control
{
    public Image Image { get; set; }
    protected Graphics graphics;
    public string FilePath { get; set; }
    protected override CreateParams CreateParams
    {
        get
        {
            CreateParams cp = base.CreateParams;
            cp.ExStyle |= 0x00000020; //WS_EX_TRANSPARENT
            return cp;
        }
    }
    protected override void OnPaintBackground(PaintEventArgs pevent)
    {
        // Don't paint background
    }
    protected override void OnPaint(PaintEventArgs e)
    {
        // Update the private member so we can use it in the OnDraw method
        this.graphics = e.Graphics;
        // Set the best settings possible (quality-wise)
        this.graphics.TextRenderingHint =
            System.Drawing.Text.TextRenderingHint.AntiAlias;
        this.graphics.InterpolationMode =
            System.Drawing.Drawing2D.InterpolationMode.HighQualityBilinear;
        this.graphics.PixelOffsetMode =
            System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
        this.graphics.SmoothingMode =
            System.Drawing.Drawing2D.SmoothingMode.HighQuality;
        if (Image != null)
        {
            // Sets the images' sizes and positions
            var width = Image.Size.Width;
            var height = Image.Size.Height;
            var size = new Rectangle(0, 0, width, height);
            // Draws the two images
            this.graphics.DrawImage(Image, size);
        }
    }
}