class Work_Rewrites_Model_Payment_Info extends Mage_Payment_Model_Info {
    public function getMethodInstance()
    {
        Mage::log("In rewrite payment info model");
        if (!$this->hasMethodInstance()) {
            if ($this->getMethod()) {
                $instance = Mage::helper('payment')->getMethodInstance($this->getMethod());
                if ($instance) {
                    $instance->setInfoInstance($this);
                    $this->setMethodInstance($instance);
                    return $instance;
                }
            }
            //return false;
            Mage::throwException(Mage::helper('payment')->__('The requested Payment Method is not available.'));
        }

        return $this->_getData('method_instance');
    }
}

<config>
        <global>
            <models>
                <rewrites>
                    <class>Work_Rewrites_Model</class>
                </rewrites>
                <payment>
                    <rewrite>
                        <info>Work_Rewrites_Model_Payment_Info</info>
                    </rewrite>
                </payment>
            <models>
        <global>
    <config>