<?php echo form_open_multipart('/jobs/delivery', array('class' => 'form-horizontal', 'id' => 'form-doc'),array('job_id' => ''));?>
<iframe id='form-doc-iframe' name='form-doc-iframe' src=""></iframe>
document.getElementById('form-doc').target = 'form-doc-iframe'; //'my_iframe' is the name of the iframe
document.getElementById('form-doc-iframe').domain = site;
document.getElementById('form-doc').submit();