This stumped for a few days and none of the solutions were viable or worked.

If you are running php-fpm with nginx

In the server{} block in www.yourdomain.com.config add:

proxy_pass_header Server;

In your PHP controller:

header("Server: Singer Sewing machine");

I needed a solution fast to pass PCI and was panicking that I only had a few days to find a viable solution. This got it done.

I could not find a way to set it in either php.ini or the fpm configs.