OS X :: Edit Mail's Previous Recipients List?

So my dad is finally switching from his beloved gmail.com web app to Mail. There is just one problem. A bunch of his contacts that he normally emails are already in Address Book. However, Gmail has a list of about 300 people that he has emailed in the past. He probably still emails about 100 of them from time to time.. I noticed Mail.app has a "Previous Recipients" list, and you can delete entries from the list or add them to address book. Is there anyway I can manually add some of the email addresses from his Gmail account into that list? In Snow Leopard, the file seems to be located in ~/Library/Application Support/Address Book/MailRecents-v4.abcdmr

I know I can just export all the contacts and put them into Address Book, but he uses his address book's all contacts field on his iPhone, and I don't want to clutter that with those email addresses. Unless there is a way of making an entry that appears in a specific address book group, but not in all contacts.