Simple Sitemap in HTML Format as Static Block for Magento

The steps I ended up using were as follows, and the comments and answers so far got me started in the right direction.

First I added a row to the "sitemap" table. Since we have multi-store set up, and because I want to keep my module store agnostic, I didn't hard code this INSERT into a MySQL migration, but just ran it on the store manually:

INSERT INTO sitemap (sitemap_type, sitemap_filename, sitemap_path, store_id)
    VALUES ('people', 'people.xml', '/sitemap/', 2);

Then I overwrote the Mage_Sitemap_Model_Sitemap model inside the global/models section in my own module's config.xml file:

<global>
    <models>
        <sitemap>
            <rewrite>
                <sitemap>Mymod_People_Model_Sitemap</sitemap>
            </rewrite>
        </sitemap>
    </models>
</global>

This overwrites any calls to Mage_Sitemap_Model_Sitemap site-wide with my custom model, but I didn't want to copy and paste too much code there. Using Petar Dzhambazov's suggestion, I used a conditional to defer to the parent class unless the sitemap_type is "people".

class Mymod_People_Model_Sitemap extends Mage_Sitemap_Model_Sitemap
{
    const PAGE_REFRESH_FREQUENCY = 'weekly';
    const PAGE_PRIORITY = '1.0';

    public function generateXml()
    {
        if ($this->getSitemapType() != 'people') {
            return parent::generateXml();
        }

        $io = new Varien_Io_File();
        $io->setAllowCreateFolders(true);
        $io->open(array('path' => $this->getPath()));

        if ($io->fileExists($this->getSitemapFilename()) && !$io->isWriteable($this->getSitemapFilename())) {
            Mage::throwException(Mage::helper('sitemap')->__('File "%s" cannot be saved. Please, make sure the directory "%s" is writeable by web server.', $this->getSitemapFilename(), $this->getPath()));
        }

        $io->streamOpen($this->getSitemapFilename());

        $io->streamWrite('<?xml version="1.0" encoding="UTF-8"?>' . "\n");
        $io->streamWrite('<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">');

        $storeId = $this->getStoreId();
        $date    = Mage::getSingleton('core/date')->gmtDate('Y-m-d');
        $baseUrl = Mage::app()->getStore($storeId)->getBaseUrl(Mage_Core_Model_Store::URL_TYPE_LINK);

        /**
         * Generate people sitemap
         */
        $changefreq = Mymod_People_Model_Sitemap::PAGE_REFRESH_FREQUENCY;
        $priority   = Mymod_People_Model_Sitemap::PAGE_PRIORITY;
        $collection = Mage::getModel('people/person')->getCollection();
        foreach ($collection as $item) {
            $xml = sprintf('<url><loc>%s</loc><lastmod>%s</lastmod><changefreq>%s</changefreq><priority>%.1f</priority></url>',
                htmlspecialchars($item->getUrl()),
                $date,
                $changefreq,
                $priority
            );
            $io->streamWrite($xml);
        }
        unset($collection);

        $io->streamWrite('</urlset>');
        $io->streamClose();

        $this->setSitemapTime(Mage::getSingleton('core/date')->gmtDate('Y-m-d H:i:s'));
        $this->save();

        return $this;
    }
}

Is there a better way, that avoids copying and pasting so much from the parent class?

You need to create rewrites in .htaccess:
How to add sitemap.xml for multistore magento

First, create a new folder called sitemaps in the root of your website, then create subfolders for each domain.
/sitemaps/domain_1/
/sitemaps/domain_2/

Then login to the Magento admin and navigate to – catatlog -> google sitemap

Create or edit the sitemap listings for each store and set the “path to sitemap” field to be the path you created for the store.

/sitemaps/domain_1/
/sitemaps/domain_2/

Update your robots.txt file. To make sure that the search engine spiders are properly directed to the new sitemaps. You may need to update or create the robots.txt file. Edit the robots.txt file and add the following lines at the top —

# Website Sitemap
Sitemap: http://www.domain_1.com/sitemaps/domain_1/sitemap.xml  
Sitemap: http://www.domain_2.com/sitemaps/domain_2/sitemap.xml

Finally, if your site uses the Apache web server engine, you should update the .htaccess file in the root of your website to direct any other sitemap requests to the proper place.
Locate the following line below the line that reads — RewriteEngine on

And add the following redirect statements below it —

# Sitemap: http://www.domain_1.com/sitemaps/domain_1/sitemap.xml
RewriteCond %{HTTP_HOST} ^.*domain_1\.com$
RewriteRule ^sitemap.xml$ sitemaps/domain_1/sitemap.xml [NC,L,R=301]

# Sitemap: http://www.domain_2.com/sitemaps/domain_2/sitemap.xml
RewriteCond %{HTTP_HOST} ^.*domain_2\.com$
RewriteRule ^sitemap.xml$ sitemaps/domain_2/sitemap.xml [NC,L,R=301]