The JSON object doesn't have an exposed API yet, so you can't manipulate it in scripts. You could however ditch it altogether work solely with scripts for your JSON needs.
First load the JSON file with AJAX, then set a local or global variable to AJAX.LastData.
Inside a script, you could then parse said variable and store the object inside the runtime for later use.
runtime.myArray = JSON.parse(runtime.globalVars.json);
That new "myArray" attribute of the runtime could then be filtered using the filter() method.