Code

public class OrgChartNode : ShapeNode, InplaceEditable

...

// in the constructor
MouseMove += OrgChartNode_MouseMove;

// implementation
Rect InplaceEditable.GetEditRect(Point position)
{
	var r = Bounds;
	r.Height = r.Height / 2;
	if (position.Y > r.Y + r.Height / 2)
		r.Y = r.Y + r.Height;
	return r;
}

DiagramItem InplaceEditable.GetDiagramItem()
{
	return this;
}

string InplaceEditable.GetTextToEdit()
{
	if (textBeingEdited == -1)
		textBeingEdited = mousePos.Y < Bounds.Height / 2 ? 0 : 1;

	switch (textBeingEdited)
	{
		case 0:
			return Title;
		case 1:
			return FullName;
	}
	return "";
}

void InplaceEditable.SetEditedText(string newText)
{
	switch (textBeingEdited)
	{
		case 0:
			Title = newText;
			break;
		case 1:
			FullName = newText;
			break;
	}
	textBeingEdited = -1;
}

private Point mousePos;
private int textBeingEdited = -1;

void OrgChartNode_MouseMove(object sender, System.Windows.Input.MouseEventArgs e)
{
	mousePos = e.GetPosition(this);
}