This is very simple. You only need to duplicate the apache directory, and all that goes with it.
Your apache2 idea will work just fine.
You don't need to rename the httpd daemon, as anytime you run apache, or httpd, you will notice a PID for every open connection that you have. This is why httpd.conf will allow you to limit the number of simultaneous connections, as so not to kill your machine if you are a serving bandwidth intensive apps, or just don't want to become the victim of a DoS attack.
As far as the rc.d is concerned, simply put the full path to the httpd that you want to start - for instance, you could have one in a dir labled 8000, and one for 8001.....etc......