# untested

package DBIx::Simple::Result::Metaperl;
our @ISA = qw(DBIx::Simple::Result);

sub map_arrays_of_hashes {
    my ($self, $column_name) = @_;
    my %arrays;
    for my $row ($self->hashes) {
        push @{ $arrays{$row->{id}} }, $row;
    }
    return wantarray ? %arrays : \%arrays;
}

...

$db->result_class = 'DBIx::Simple::Result::Metaperl';

my %arrays_of_hashes = $db->query(...)->map_arrays_of_hashes('id');