Thanks for the tip. Creating a custom event is of course one way to go, but being the lazy programmer that I am, I don't want to spend my time writing such an event simply to append an email recipient.
For now, I've simply hacked the eZShopOperationCollection::sendOrderEmails and appended a recipient.
It seems to me that it should be possible to define recipients of the order confirmation email, or admin recipients in general for that matter, as an array.
We have a general purpose event to send emails. However, I gave it to do to an inexperienced developer, and the code is not good enough to dare offer it as a contribution.
Basicaly, the idea is that the event as a template parameter. You set it to "confirmorder" and on this template, you set-blocks the recipients and the subject and write the body of mail.