I tried to install the dashboard under a subdirectory on my existing server and found that although there are three places in the configuration that allow the specification of the base_url
$base_url = 'http://myserver.myagency.gov/iddash'; // NO trailing slash!
$conf['ITDashboard']['appURL'] = "http://myserver.myagency.gov/webapp"; // Base URL for the website for public users
$conf['ITDashboard']['loggedInAppURL'] = ""; //Base URL for the website for logged in users
You can't really put the application in a subdirectory since most of the links to images and pages have a '/' in the front of the page. This made me sad:(