skip processing html and page
based on comments above and my own edits, i came up with this

function my_page_callback() {
    $output =  array(
        'template' =&gt; array(
            'data'      =&gt; array('dummy'=&gt;true),
            '#theme'    =&gt; 'my_theme'
        )
    );
    print drupal_render($output);
    drupal_exit();
}


that goes straight for the beef: print the output. it does however use the templating system to create that output. it does not, i think, do all the preprocessing that would otherwise happen.