is it possible to have diferent php.ini configurations for each
virtualhost,
like .htaccess while using mod_php with apache?
If not, there´s any workround?
You can run php-cgi instances as FastCGI servers with different
configurations (using -c flag to point to different .ini files) on
different ports, then refer to them specifically inside server {}
contexts in nginx config. e.g.
location ~ .php$ {
fastcgi_pass 192.168.0.1:10002;
}other stuff …
}
I was afraid you said that. 
I´ll try the new PHP 5.3 .user.ini to see if it works with fastcgi.
you could manage your instances using php-fpm, and it allows for
certain php.ini directives to be overridden in the conf. heck, it
might even allow (or maybe ask andrei nicely) to use a completely
different .ini for each worker pool.
this .user.ini thing i have not heard of yet - i need to go look that
up myself, that sounds interesting!
PHP 5.3 .user.ini
and
[path=/var/www/…] in php.ini works like a charm!