In iCal, how can I send multiple email invitations for a single event to one invitee who has multiple email addresses?

In the "Invitees" field of an event in iCal 4.0.4, I can list my wife from her Address Book card, and choose either her work or personal email address; but I cannot add her *again* and choose the *other* email address, so that she receives it both at work and on her iPhone.

I read about one (very awkward) workaround, where you create in Address Book a new email field for the person, in which all of the person's emails, separated by commas, are entered in one field. I have not tried it, yet, because it seems as if this addressing feat is fairly obvious and should be a really easy thing to do in iCal.