Works well for me, thank you for the tip!
Just one little thing, the header has already been printed so I added this little bit of code
Add this to config.php
$CFG->customfrontpageinclude = 'local/plugin/index.php'; // No leading slash.
Then in local/plugin/index.php
<?php
...
// Add this to your page setup.
if ($PAGE->state <= moodle_page::STATE_PRINTING_HEADER) {
// If calling from the front page then it already has a header so don't print it.
// Otherwise print as normal,
echo $OUTPUT->header();
}
...
echo $OUTPUT->footer();
// Add this to the end of the page.
exit(); // This forces the frontpage to stop at this point so nothing else is printed.