If you can't use PHP to force HTTPS, you can use mod_rewrite instead. Toss this in an .htaccess file in the web root of your site:
RewriteEngine On
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$ https://www.domain.com/$1 [R,L]
Or, if it needs to be forced only for a certain folder:
RewriteEngine On
RewriteCond %{SERVER_PORT} 80
RewriteCond %{REQUEST_URI} somefolder
RewriteRule ^(.*)$ https://www.domain.com/somefolder/$1 [R,L]
