Excellent, that's exactly what I was looking for. Now I just need to figure out how to apply it properly, and what constraints I'll need to impose on the users.

Update: in searching for caveats to Symbol::delete_package, I encountered Mark-Jason Dominus's scrub_package:

sub scrub_package {
    no strict 'refs';
    my $pack = shift;
    die "Shouldn't delete main package"
        if $pack eq "" || $pack eq "main";
    my $stash = *{$pack . '::'}{HASH};
    my $name;
    foreach $name (keys %$stash) {
        my $fullname = $pack . '::' . $name;
        # Get rid of everything with that name.
        undef $$fullname;
        undef @$fullname;
        undef %$fullname;
        undef &$fullname; # or *$fullname = sub { }
        undef *$fullname;
    }
}
[download]

This is very similar to what delete_package does, at least in 5.8.1, but both have the unfortunate side effect of also deleting any imported subroutine -- so if &mypackage::glort is aliased to &main::glort, then you won't be able to call main::glort() after deleting "mypackage". If you use the above commented out line (*$fullname = sub {}), you will avoid this issue.

Which says to me: "here be dragons". But I guess I knew that already. I hope they're friendly ones.

Update2: But in actually testing the above problem, it does not appear to happen with 5.8.1's Symbol::delete_package (version 1.04). So never mind. It's only a problem with the above code. Life is good.