Add follwing code into _prepareForm() function.
$fieldset->addField('professor_firstname', 'text', array( 'label' => Mage::helper('deskcopy')->__('Professor First Name'), 'readonly' => true, 'name' => 'professor_firstname', ));
OR $fieldset->addField('professor_firstname', 'hidden', array( 'label' => Mage::helper('deskcopy')->__('Professor First Name'), 'after_element_html' => '<tr><td><label for="title">Professor First Name</label></td> <td>' .$data['professor_firstname'] . '</td></tr>', ));