Joomla! 2.5 Can't change task from within top level controller of my component

Question

I built a Joomla component a while ago which presents a disclaimer page immediately after logging in whereby the user has to select "I Agree" before going to the restricted site content.

The component is called com_rsdisclaimers and it has a master controller ~/coontroller.php and another (sub)controller in ~/controllers/rsdisclaimer.php defined as class RsdisclaimersControllerRsdisclaimer extends JControllerForm. The sub controller has a task/method called agree() which sets a session variable and redirects.

This all works okay in that a disclaimer is displayed and when the user clicks "agree", the sub controller task "agree" is called which sets a session variable and redirects. However I am trying to allow users to bypass this screen (component) if they have previously "agreed" to the terms. I am using JUser::getParam()/JUser::setParam() to do provide this persistance.

My design is to add logic at the component root file (~/rsdisclaimer.php) which the first checks to see if the user has the parameter already set. If so , I am trying to override and run the "agree" task straight away to handle the redirect rather than displaying the component's disclaimer page. However no matter what I do, changing the 'task' to 'agree' is simply not working on the first visit to the component after logging in on account that I and getting the master controller instead of the sub controller. How do I explicitly get a handle to the subcontroller so I can call the agree task?

Here is my top level php file:

<?php
/**
 * @version     1.0.0
 * @package     com_rsdisclaimers
 * @copyright   Copyright (C) 2011 Chris Walsh. All rights reserved.
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */
defined('_JEXEC') or die;

// Include dependancies
jimport('joomla.application.component.controller');

// NOTE TO SELF: If we called JRequest::getVar('task','') at this point, we
// might get a response of "rsdisclaimer.agree".  However, when we
// call the same function after performing JController::getInstance('Rsdisclaimers')
// the task returned will now simply become 'agree'.
// 2014-11-20 | Chris Walsh 

// Test to see if the user has previously 'agreed'...
$user       = JFactory::getUser();
$accepted   = $user->getParam('rsdisclaimer.accepted', '0');
echo "<pre>JCOMPONENT_BASE: accepted={$accepted}; task={$task}</pre>";
if($accepted == '1')
{
    // Load the sub controller and jump straight to agree (redirects etc.)
    // !! THIS IS NOT WORKING!!  CAN'T GET THE SUB CONTROLLER
    $task = 'agree';
    $task = 'rsdisclaimer.agree';
    $controller = JController::getInstance('Rsdisclaimers');
    $controller->execute($task);
    $controller->redirect();
}
else
{
    // Execute the task
    $controller = JController::getInstance('Rsdisclaimers');
    $controller->execute(JRequest::getVar('task',''));
    $controller->redirect();
}

The agree method in ~/controllers/rsdisclaimer.php works IF it actually gets called:

<?php
/**
 * @version     1.0.0
 * @package     com_rsdisclaimers
 * @copyright   Copyright (C) 2011 Amy Stephen. All rights reserved.
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */
defined('_JEXEC') or die;

jimport('joomla.application.component.controllerform');

/**
 * @package     Joomla.Site
 * @subpackage  com_rsdisclaimers
 */
class RsdisclaimersControllerRsdisclaimer extends JControllerForm
{
(snip)
    /**
     * Method to deal with the user selecting "agree".
     *
     * @return  void
     * @since   1.6.1
     */
    function agree()
    {
        // Check for request forgeries.
        JRequest::checkToken() or jexit(JText::_('JINVALID_TOKEN'));

        // Set the session token which the plugin 'realsensedisclaimer' will check for
        $session = JFactory::getSession();
        $session->set('RealsenseDisclaimer', true);

        // Set the agree parameter if not already set so we don't ask again
        $user       = JFactory::getUser();
        $accepted   = $user->getParam('rsdisclaimer.accepted', '0');
        if($accepted == '0')
        {
            $user->setParam('rsdisclaimer.accepted', '1');
            $user->setParam('rsdisclaimer.acceptedDate', '2014-11-20');
            $accepted = $user->getParam('rsdisclaimer.accepted', '0');
        }

        // Redirect them to the nominated location
        $app = JFactory::getApplication();

        $url = 'index.php?option=com_content&view=article&id=1110&Itemid=101';
        $app->redirect(JRoute::_($url, false));     
    }
(snip)
}

Can anyone advise how I can get a handle to the sub controller rather than the master controller?

Thanks.