it's possible to get shoutcast streaming audio servers to register relay servers without going through the main shoutcast.com directory server.
you won't be listed on the shoutcast.com directory of course, but this is assuming you don't want to -- or can't. maybe they'll close the directory site someday (or it's just down for a while) - and you still need to get shoutcast to send users to your relay servers.
watch the traffic between shoutcast application and yp.shoutcast.com. it's just HTTP traffic that's pretty easy to parse, which is good! you can make a virtual web server with a pages that contain the data (a simple list) of your relay sites, just mimic how the directory server responds.
next, you'll need to set up a virtual web server to accept the yp.shoutcast.com host name. then, you'll have to make a local entry for the yp.shoutcast.com dns in your hosts file to point to the ip of your web server. you'll have to set the dns, in the hosts file wherever you're running shoutcast servers (to point to the web server). this wouldn't cover people relaying your site without consent, or you can try to tell them do make the entry, to get on the relay list.
just make sure you have the html file format right, and that should do it. i've tested it out, and it works - but i use the directory server myself. i'd keep this handy in case anything happens to the directory server - just as a backup really.
send email / comments if you need further assistance to figure this out.