The script is:
Code:
<script>if(!location.hash)location.hash='xl_xr_page_home';</script>
but you will have to adjust xl_xr_page_home to xl_xr_page_... whatever the name of the page is that you want to be shown first.
You can put the script to the head of the site, a page or a placeholder, it doesn't matter when using a supersite.

Acorn, there are always multiple ways to do something in javascript.