I think you could edit the file includes/cron/reminder.php, and look for this line:
Code:
vbmail($userinfo["$userid"]['email'], $subject, $message, true);
which is near the end of the code. Change it to:
Code:
vbmail($userinfo["$userid"]['email'], $subject, $message, true, '', 'Bcc: other@mail.com');
where you would of course change the email address to the one which will get the copies. If you want. I haven't tested this so you'll have to see if it works.
I think the same code sends calender event reminders, so you may get copies of those as well. There must be a way of checking that, which we could probably figure out if that's a problem for you.
Edit: Well,l I'm not sure if that will work for Bcc. If not, you might be able to Cc (but of course the user will see the additional address), or else you might instead have to copy the vbmail line and change the first parameter to your email address, so that you actually send two emails.