Code

(in diagram constructor/init:)

            TransferDiagram.LinkShape = LinkShape.Cascading;
            TransferDiagram.LinkCascadeOrientation = Orientation.Horizontal;
            TransferDiagram.LinkSegments = 3;
            TransferDiagram.RoundedLinks = true;
            TransferDiagram.RoundedLinksRadius = 20;

(drawing by:)

 internal void DrawLink(DiagramNode from, DiagramNode to)
        {
            var link = new DiagramLink(TransferDiagram, from, to); //{ StrokeThickness = linkstrokethickness, Stroke = linkstroke };
            link.StrokeThickness = 10;
            link.Stroke = DetailDiagram.sBrGrayish;
            link.HeadShape = ArrowHeads.None;
            TransferDiagram.LinkSegments = 3;
            //make handles invisible:
            link.HandlesStyle = HandlesStyle.Custom;
            //link.Effect = ActiveNodeEffect; //looks horrible!
            //link.AutoRoute = true; //awful..
            TransferDiagram.LinksDrawn = true;
            TransferDiagram.Links.Add(link);
        }