I think your latest graph has taken Graph Builder built in functionality to it's max. To go where you seem to want to take it, I think you need to study up on the ability to add any graphical items to Graph Builder or any other of the graphical outputs, using the adding of graphics scripts to the outputs frame boxes. The interactive form of this, is surfaced by right clicking on a graph and selecting "Customize". This entrance to the graphical scripting world in JMP, provides one with some sample templates and scripts. However, this simple introduction, can be expanded within the JSL environment, to do just about anything you want in your graph.
I suggest you read the Scripting Guide, but that is a pretty big bite. So at a minimum, you need to read the section on Scripting Graphs in the Scripting Guide.
Jim