Normally, on SuExec Enabled Server, you can create php.ini in your account to customize php settings for your account. If php.ini is created under an account with customize php setting and it doesn’t work for you, then this is because override is disabled in /opt/suphp/etc/suphp.conf

This forces suphp to use the php.ini from /usr/local/lib/
You can comment these lines and then restart Apache to resolve the issue.

[phprc_paths]
;Uncommenting these will force all requests to that handler to use the php.ini
;in the specified directory regardless of suPHP_ConfigPath settings.
;application/x-httpd-php=/usr/local/lib/
;application/x-httpd-php4=/usr/local/php4/lib/
;application/x-httpd-php5=/usr/local/lib/

Done