Have a variable "site url" on the directive snippet in order to create a directive snippet for FastCGI Cache

Hi, I'm just trying to have a directive snippet for FastCGI Cache but I see that available variables are not useful at all. I usually use domain name, that is a current variable on the nginx_vhost.conf but this variable is not available on the directive snippet configuration.

fastcgi_cache_path /var/cache/nginx/<tmpl_var name='domain'>/ levels=1:2 keys_zone=<tmpl_var name='domain'>:100m inactive=180m;

Is it possbile to add it?

Thanks!