Found this thread which, as of nine months ago, indicates that what I want to do isn’t possible. Not sure if the new theme system with 1.7 should have changed anything though.
If this is indeed a missing feature and not a bug, I’ll probably do a feature request…the current system is rather unintuitive, no?
In the meantime, where would I have to go in the code to get the register and activate pages to load my anti-sidebar template?