Argh - gform_pre_render again

You may want to merge this into my previous thread, as I thought I'd solved it, but haven't :(

Problem arises when unsetting a required field - it's still required. So, I need something extra here, but not sure what.

function sd_hide_or_require_insured($form){
	$insuredfield = array('Insured');
	global $post;
	$needsinsurance = get_post_meta($post->ID,'_sd_prod_insurance',true);
	if ($needsinsurance==1) {
		//make the field required  - but how?
	} else {
		foreach($form['fields'] as $key=>$field) {
			if(in_array($field['label'], $insuredfield)) {
				unset($form['fields'][$key]);
//or alternatively make it not required if value is 0,  as well as unsetting
			}
		}
	}
    return $form;
}

Any help really appreciated.