there are a couple of things you can try:
in httpd.conf find the line that begins with "DirectoryIndex" and replace it with "DirectoryIndex disabled" this way apache will not server default files like index.html and just list files. however you can explicitly request it if you want.
if default document setting is important to you, you can also configure apache to listen to another port and setup a virtual host on that port and do the same thing with "DirectoryIndex" for virtual host, this way you have two ports , one that serves default documents and one that only list files.
if you want to use only one port for this , you can try no. 2 option and then set a proxy that sends all requests that begin for example with /list/ to the other virtual host, this way you work on one port and if you want list of files instead of writing "/myserver/mydirectory" you request "/list/myserver/mydirectory"
hope it helps.