Code

private void OnLinkCreated(object sender, LinkEventArgs e)
{
	e.Link.CustomDraw = CustomDraw.Additional;
	e.Link.TextBrush = null;
	e.Link.Text = "test";
}

private void OnDrawLink(object sender, DrawLinkEventArgs e)
{
	e.Graphics.DrawText(new FormattedText(e.Link.Text,
		CultureInfo.CurrentCulture, FlowDirection.LeftToRight,
		new Typeface(e.Link.FontFamily.Source), e.Link.FontSize, Brushes.Black),
		e.Link.Bounds.Location + new Vector(10, 10));
} 

Code

private void OnDrawLink(object sender, DrawLinkEventArgs e)
{
	var link = e.Link;
	var points = link.ControlPoints;
	var origin = points[0];
	var dest = points[points.Count - 1];
	bool vertical = points.Count == 2 && Math.Abs(origin.X - dest.X) < 5;
	if (vertical)
	{
		double textWidth = diagram.MeasureString(link.Text, link, 1000).Width;
		e.Graphics.DrawText(new FormattedText(link.Text,
			CultureInfo.CurrentCulture, FlowDirection.LeftToRight,
			new Typeface(link.FontFamily.Source), link.FontSize, Brushes.Black),
			new Point(origin.X - textWidth - 10, (origin.Y + dest.Y - link.FontSize) / 2));
	}
	else
	{
		...
	}
}