Thanks to @MichaelBerkowski's help, here's a simple tested snippet with the solution to the question.
<?php
/**
* Include code base from outside public_html to be accessible to scripts
* that are accessible via web browser
*/
// defines the path of the codebase
define("APPLICATION_PATH", realpath('/usr/apps/myapp/controllers/'));
// defines the working directory of the, i.e., index.php file
define("CURRENT_PATH", getcwd());
// create the paths array
$paths = array(APPLICATION_PATH, CURRENT_PATH);
// set the include path configuration option for the duration of the script
set_include_path(implode($paths, PATH_SEPARATOR));
// include a script file located in the realpath
include('ReporterClass.php'); // located in /usr/apps/myapp/
// instantiate the class
$report = new Reporter();
// test output
echo "<h3>".$report->showReport("Sample Report")."</h3>";
?>