Well, I've never used Ghost Blog myself, but as far as I can tell what you want to do sound a lot like the Virtual Domain feature, present both in Apache and NGINX.
You may find more information here: https://www.digitalocean.com/community/articles/how-to-set-up-nginx-virtual-hosts-server-blocks-on-centos-6
With Virtual Domains, you might have several different domains (including, but not restricted to sub-domains to domains you own.) being processed by the same server.
Ex.: www.virtdom1.com and www.virtdom2.com both resolve to a droplet with IP 22.214.171.124 where "virtdom1.com" is @ "/usr/local/nginx/html/virtdom1.com" and "virtdom2.com" is @ "/usr/local/nginx/html/virtdom2.com". You are virtually unrestricted regarding to how many domains and/or sub-domains you may host at one instance.
Using Virtual Domains, NGINX acts also as a HTTP proxy, forwarding each domain request to it's due folder in the web server.
Hope this helps ya! :)
This tutorial shows you how to set up virtual hosts. Virtual Hosts are used to run more than one website or domain off of a single server and IP address. When used with nginx, virtual hosts are called Server Blocks. This tutorial covers setting up server blocks on a Centos server.