[Koha] Send all notices to all available eMail addresses

Hi all, we are using Koha in our school library and we have the following "problem". We checkout books to all of our students starting from preschool. Especially the younger once don't have a personal eMail address. So we like to send notices (checkouts, checkins, overdues...) to both parents. As far as I understand Koha it send the notices only to one address. We could put in one of the parent's email, but we like to inform both. I've read that overdue_notices.pl has an repeatable --email parameter. Where can I change it to send the notice to both parents? Are there other ways to solve this problem or is it just not possible? I'm thankful for any hints. Regards, Stephan