my $namespace = \%GMPN::Database::Table::;
my %inject = (
    pre_insert => sub { ... },
    pre_update => sub { ... },
);

for my $subpkg (qw[org user group foo bar]) {
    my ($method, $code);
    $namespace->{"$subpkg::"}->{$method} = $code
        while ($method, $code) = each %inject;
}