Код 2012 года.

add_action('wp_head', 'adjust_sticky_footer');
function adjust_sticky_footer() {
if(is_admin_bar_showing()) { ?>
<style type="text/css">
.footer { /* Adjust selector according to your theme */
bottom: 28px;
}
</style>
<?php
}
}

I'm assuming your footer already has position: relative assigned to it, as per the example on the link you've provided.