How to set a Reference Line on each page with Page option in Graph Builder?

[#1]

The following script plots some charts with the page option in graph builder? How to I set a horizontal reference line, for each chart, say at Weight = 80Kg and label it (80kg) using JSL?

(I need the reference line to remain even if there is a change in the number of charts plotted)

Names Default To Here(1); 
dt = open("$SAMPLE_DATA/Big Class.jmp");
gb = dt << Graph Builder(
	Size(528, 2954),
	Show Control Panel(0),
	Variables(X(:height), Y(:weight), Page(:age)),
	Elements(Points(X, Y, Legend(15)), Smoother(X, Y, Legend(16)))
);

[#2]

Names Default To Here(1); 
dt = open("$SAMPLE_DATA/Big Class.jmp");
gb = dt << Graph Builder(
	Size(528, 2954),
	Show Control Panel(0),
	Variables(X(:height), Y(:weight), Page(:age)),
	Elements(Points(X, Y, Legend(15)), Smoother(X, Y, Legend(16)))
);

axis = gb << XPath( "//AxisBox" );
Summarize( page = By( :age ) );
axis[2::(2*NItems( page ))::2] << Add Ref Line( 80, "Solid", "Red", "Reference" );

[#3]

@Mark_Bailey  Stops working for me (JMP 16.2) if I invoke Local Data Filter on Age after plotting, as below