a custom module for drupal that creates a popup interstitial. This module uses Drupal's entity metawrapper api, and dynamic db queries. See full module here https://github.com/devupable/popup-interstitial-drupal

php interstitial drupal module

<?php
/**
 * @file
 * Sample Bean Content to fill out icttemplate
 */
//http://www.pixelite.co.nz/article/how-use-entity-metadata-wrappers-drupal-7/
//https://www.drupal.org/dynamic-queries
//http://ovistaoa.dev/devel/php
include_once 'idi_interstitial.features.inc';
include_once 'idi_interstitial.features.field_base.inc';
include_once 'idi_interstitial.features.field_instance.inc';
include_once 'idi_interstitial.features.user_permission.inc';

function idi_interstitial_install()
{
    if (!module_exists('interstitial')) {
        $modules = array('interstitial');
        module_enable($modules);
        idi_interstitial_load_fields();
    }
}

function idi_interstitial_uninstall()
{
    if (module_exists('interstitial')) {
        $modules = array('interstitial');
        module_disable($modules);
    }
}

function idi_interstitial_enable()
{
    $bean_ids = array();
    global $language;
    //global $theme;
    $theme = variable_get('theme_default', NULL);

    idi_interstitial_bean_type_record('interstitial', 'interstitial');

    foreach (idi_interstitial_info() as $bean_content) {
        $bean = bean_create(array('type' => 'interstitial'));
        $bean_wrap = entity_metadata_wrapper('bean', $bean);
        $bean_wrap->label->set($bean_content['label']);
        $bean_wrap->title->set($bean_content['title']);
        $bean_wrap->language($language->language)->field_interstitial_copy->set(array(
            'value' => $bean_content['field_interstitial_copy'],
            'format' => 'full_html',
        ));
        $bean_wrap->field_external->set(array(
            'url' => '#',
            'title' => 'Ok',
            'attributes' => array(
                'title' => 'close this window and proceed to the external site',
                'class' => 'external, button',
            )
        ));
        $bean_wrap->field_internal->set(array(
            'url' => '#',
            'title' => 'Cancel',
            'attributes' => array(
                'title' => 'cancel request, remain on this page ',
                'class' => 'internal, button',
            )
        ));
        $bean_wrap->save();
        $bean_ids[] = $bean_wrap->bid->value();
        //set variable to store bean ids
        variable_set('idi_interstitial_ids', $bean_ids);

        idi_interstitial_position(
            array(
                'bid' => $bean_wrap->bid->value(),
                'region' => $bean_content['region'],
                'weight' => $bean_content['weight'],
                'status' => $bean_content['status'],
                'delta' => $bean_content['delta'],
                'theme' => $theme,
            ));
    }
    user_role_grant_permissions(DRUPAL_ANONYMOUS_RID, array('view any interstitial bean'));

    // Flush cache
    cache_clear_all();
}

function idi_interstitial_disable()
{
    $bids = variable_get('idi_interstitial_ids', array());
    entity_get_controller('bean')->delete($bids);

    idi_interstitial_bean_type_record('interstitial', 'interstitial', false);

}

function idi_interstitial_load_fields()
{
    foreach (idi_interstitial_field_default_field_bases() as $field_base) {
        field_create_field($field_base);
    }
    foreach (idi_interstitial_field_default_field_instances() as $field_instance) {
        field_create_instance($field_instance);
    }

    foreach (idi_interstitial_field_default_field_instances() as $field_instance) {
        field_create_instance($field_instance);
    }

}

function idi_interstitial_info()
{
    $site_name = variable_get('site_name');
    $bean_content = array(
        'interstitial' => array(
            'label' => 'interstitial',
            'title' => 'interstitial',
            'region' => 'hidden',
            'delta' => 'interstitial',
            'weight' => 1,
            'status' => 1,
            'field_interstitial_copy' => '<p>' . t('This link will take you to a website to which the ') . $site_name . t(' Privacy Policy does not apply. We encourage you to read the Privacy Policy of every website you visit.') . '</p>' .
                t('You may click the OK button to access the requested website or click Cancel to remain on the current page.') . '</p>',
        ),
        'interstitial_iframe' => array(
            'label' => 'interstitial_iframe',
            'title' => 'interstitial_iframe',
            'region' => 'hidden',
            'delta' => 'interstitial-iframe',
            'weight' => 2,
            'status' => 1,
            'field_interstitial_copy' => '<p>' . t('This link will take you to a part of the website to which the ') . $site_name . t(' Privacy Policy does not apply. We encourage you to read the Privacy Policy of every website you visit.') . '</p>' .
                t('You may click the OK button to access the requested page or click Cancel to remain on the current page.') . '</p>',
        ),

    );
    return $bean_content;
}

function idi_interstitial_position($params = array())
{
    //https://api.drupal.org/api/drupal/includes!database!database.inc/function/db_update/7
    //define region and weight
    db_update('block')
        ->fields(array(
                'status' => $params['status'], 'region' => $params['region'], 'weight' => $params['weight'])
        )
        ->condition('delta', $params['delta'])
        ->condition('theme', $params['theme'])
        ->execute();

}

function idi_interstitial_bean_type_record($name, $label, $insert = true)
{
    if ($insert) {
        db_insert('bean_type')
            ->fields(array(
                    'name' => $name, 'label' => $label)
            )
            ->execute();
    } else {
        db_delete('bean')
            ->condition('type', $name)
            ->execute();

        db_delete('bean_type')
            ->condition('name', $name)
            ->condition('label', $label)
            ->execute();
    }
}