Code

void MoveLink(DiagramLink link, double dx, double dy)
{
	var offset = new Vector(dx, dy);
	var points = link.ControlPoints;
	for (int i = 0; i < points.Count; i++)
		points[i] += offset;
	link.UpdateFromPoints();
}

diagram.CommandBindings.Add(
	new CommandBinding(Diagram.NavigateLeft, (sender, args) =>
	{
		var link = diagram.ActiveItem as DiagramLink;
		if (link != null && !link.IsConnected)
			MoveLink(link, -8, 0);
	}));

diagram.CommandBindings.Add(
	new CommandBinding(Diagram.NavigateUp, (sender, args) =>
	{
		var link = diagram.ActiveItem as DiagramLink;
		if (link != null && !link.IsConnected)
			MoveLink(link, 0, -8);
	}));

diagram.CommandBindings.Add(
	new CommandBinding(Diagram.NavigateRight, (sender, args) =>
	{
		var link = diagram.ActiveItem as DiagramLink;
		if (link != null && !link.IsConnected)
			MoveLink(link, 8, 0);
	}));

diagram.CommandBindings.Add(
	new CommandBinding(Diagram.NavigateDown, (sender, args) =>
	{
		var link = diagram.ActiveItem as DiagramLink;
		if (link != null && !link.IsConnected)
			MoveLink(link, 0, 8);
	}));