I appreciate the responses, but I guess I'm either not phrasing my question clearly or I'm not understanding the relevance of your responses. I know how to configure the host file and that works just fine.
When I create a website linked to the external IP address, ISPConfig creates the following folder structure to store the web content to be served:
I also want users connecting over the internal network to be able to view the content in that same folder, but the only way I've found in ISPConfig to do that is to create a second website linked to the internal IP address, which results in a second folder structure
In order to what I want, it's easy enough to go in with a text editor and manually change the server directory directive in the .vhost file for the second website to point to the folder
I've done that, and what I want to do seems to work just fine (although I haven't tested in very rigorously yet.) It just seemed like there should be some way to do the same thing using that nice ISPConfig interface.
Hopefully that makes my question a little clearer.