Code

RectangleF r = link.Origin.Bounds;
float centerx = r.Left + r.Width / 2;
float dist = 16;
SetLinkPoints(link,
	new PointF(centerx, r.Top),
	new PointF(centerx - dist, r.Top - dist),
	new PointF(centerx + dist, r.Top - dist),
	new PointF(centerx, r.Top));

}

private void SetLinkPoints(DiagramLink link, params PointF[] points)
{
	link.AutoRoute = false;
	link.Style = LinkStyle.Bezier;
	link.ControlPoints.Clear();
	link.ControlPoints.AddRange(points);
	link.UpdateFromPoints(false, true);
}