Allow customer to independently set additional php directives

Hi all,

is there any way in making independent a customer to add / override uncommon PHP parameters
(ie. max_input_vars) for a particular vhost, if the domain is set in PHP-FPM ?

I know that the administrator account have to "Additional configuration directives" available in the PHP seciton , but a customer can not have that section enabled.

In addition the option to add values using .htaccess ("php_value") does not work with a PHP-FPM domain (error 500).

Thank you in advance.