Intercept and modify core method results

I have multiple custom controllers working great, but would like add a controller method to modify the output of core.get_page before output. How can I, from within my custom controller, call core.get_page and modify the output object before it is converted to JSON for the client?

I tried instantiating JSON_API_Core_Controller in my custom controller, but this class is unknown at this point of execution. I also tried to require_once the core.php file, but it seems its dependencies are not loaded.

Thanks!

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