A friend of mine has shown me how Sophos UTM is managing this.
You have a page, where you configure your Webservers (the Server where the ProxyPass would redirect to) and the Pages (the ServerName of the VirtualHost as well as the Ports).
This is how it looks like:
The “Website”-Management (“virtual Webserver”):
Edit a Website:
And managing the Webservers (“Real Webservers”):
Maybe helpful for some inspiration 