Skip 'port is in use' check

I’m having a NAT vps. It means that I don’t have access on all port, just a few. My provider does support HAProxy which will proxy requests to my domain on port 80 to my vps. That way, I can set up webserver to work on port 80 from my domain. But ghost start always check if a port is in use. In my case is port 80, yes, it’s used by host machine. So is there anyway I can port check?