I'm also using apache to proxy ACS sites. Basically I have aolserver listening on localhost only, and Apache is listening on the external interface port 80, the virtual server directives read the host-header information and proxy to the appropriate server on localhost.
After significant research and experimentation, I find this to be the easiest and most flexible method to do virtual hosting on one IP address.
I'd be glad to provide sample configuration files if you'd like.