session timeout with php_value session.gc_maxlifetime

After my users log in, the $_SESSION["logged_in"] expires after inactivity of the default 24 mins (1440 secs) and logs them out.

I want to extend this to 2 hours (7200 secs), but adding the below into my .htaccess is not doing it.

php_value session.gc_maxlifetime 7200

How can I extend the session timeout to 7200 with confidence that it is kicking in?
I want to be able to do it in the .htaccess as I do not want to change it server wide in my php.ini

Thanks in advance.

I once heard that you can have individual php.ini files in seperate directories. You might want to consider that option.