Firing custom events from individual .jsx to be picked up by panel extension

Is it possible for an external script to trigger a custom event defined in an (open) extension panel?

I tried the following but get this error when it tries to load the PlugPlugExternalObject - I assume this is no longer supported?:

IOError: File or folder does not exist

My code:

In index.js of the extension:

var cs = new CSInterface();
cs.addEventListener("myCustEvent", function(evt) {
    alert('Data from the JSX payload: ' + evt.data);
});

customEvent.jsx:

try {
    var xLib = new ExternalObject("lib:\\PlugPlugExternalObject");
} catch (e) {
    alert("xLib create failed: " + e);
}
var f = File("/Path/To/A/File.psd");
try {
     app.open(f);
     if (xLib) {
         var eventObj = new CSXSEvent();
         eventObj.type = "myCustEvent";
         eventObj.data = "some payload data...";
         eventObj.dispatch();
     }
} catch(e) {
     alert("try failed: " + e);
}

Thanks!

(edit: fixed formatting)

Post moved from Photoshop Scripting to Extensions / Add-ons Development. [Moderator]