Use existing Gravity Forms notification on non-form data

notify.php

<?php
  $form_id      = 12; // Or whatever form ID has the notificaiton you're after 
	$form         = GFAPI::get_form( $form_id );
	$notification = end( $form['notifications'] ); // Just an easy way to get the notification I wanted. YMMV.
	$lead         = array(
		'id'         => wp_generate_password( 64, true, true ), // Normally, this would be the Lead ID. Not necessary for us.
		'form_id'    => $form_id,
		'source_url' => 'https://site.com/',
		'status'     => 'active',
		'1.3'        => $args['first_name'], // YMMV on these args - set them to whatever your form sets them to be.
		'1.6'        => $args['last_name'],
		'2'          => $args['user_email'],
		'4'          => $args['term_id'],
		'5'          => $args['user_pass'],
		'1.2'        => '',
		'1.4'        => '',
		'1.8'        => ''
	);

	GFCommon::send_notification( $notification, $form, $lead );
}