The volcano is already a special link, to get you to the Myst V Descent.
However tha hard-coding we read about is what happens when you are panic linking: Whether you are linking to Relto or spawning back to your link-in point.
Anyway, I think I got it working the way we want it: When you get a new avatar, you don't have a book attached, but you can chat and type KI commands. If you /jump -5, it will eventually warp you up. If you collect your Relto book, you correctly get it and can still chat, but panic-linking is now a real link to your Relto. You can then get your KI. Typing "/removereltobook" removes it permanently until you get your KI again.
Only drawback is that if you use /removereltobook without having collected the KI, it will give you back the book whenever you link to Relto. I doubt anyone would even have noticed that though
I will still block the Myst V Descent till you get your Relto book though, in order to test this change. If the next Offline KI shows no problems, I might change it to no longer depend on a Relto book.