Code

private Dictionary<DiagramLink, PointCollection> originalPoints;
private RectangleF startPos;

private void diagram_NodeStartModifying(object sender, NodeValidationEventArgs e)
{
	startPos = e.Node.Bounds;

	originalPoints = new Dictionary<DiagramLink, PointCollection>();
	foreach (DiagramLink link in e.Node.GetAllLinks())
		originalPoints[link] = link.ControlPoints.Clone();
}

private void diagram_NodeModifying(object sender, NodeValidationEventArgs e)
{
	float dx = e.Node.Bounds.X - startPos.X;
	float dy = e.Node.Bounds.Y - startPos.Y;

	foreach (DiagramLink link in e.Node.OutgoingLinks)
	{
		if (link.Destination is DummyNode)
		{
			PointCollection points = originalPoints[link];
			for (int i = 1; i < points.Count; i++)
			{
				PointF p = points[i];
				p.X += dx;
				p.Y += dy;
				link.ControlPoints[i] = p;
			}
			link.UpdateFromPoints();
		}
	}
}