Actually SITEROOT has a different meaning: it allows you to install and use the script in a subfolder on your site... for example if the site is site.com (or
www.site.com), the script can be installed in the "games" folder. To make it accessible at site.com/games/ (
www.site.com/games/) you just need to set the SITEROOT=/games/.
As for your question, RewriteCond in htaccess - is the only solution, and this works perfectly.