I think it's safe to work under the assumption that a DJ works for one station. If not, there's nothing to stop them from opening a second account, with a new userid. I think your registration form suggestion is a good one. Although there would need to be a way for the user (DJ) to modify their registration information. After all, some DJs do change jobs ...
I spent a little time last night with the relational.txt page and I'm not too intimidated with it. Your instructions seem fairly clear - although I'm not certain if they work the same for the user-friendly html.pl as they do for the original html.pl.
Rich