You can buy any Entertainment Book, even the ones from Australia, to get the card that gets you the HoJo discount.
You can get the big HoJo discount if it is offered during your stay. If it's NOT offered during your time, they have a special smaller discount they offer anyway, if you have the card (at checkin).
hojoanaheim has message boards of their own (they sometimes change the links of their board, it seems, so the best way I can tell you where it is is: hojoanaheim.com and find "join the discussion" or something like that, which will take you to their boards) and they have a whole forum on discounts. Look for the Ent Rate discount section. They have a list that is kept updated.
They have been known to add dates even just 3 days before...I totally missed out on staying there at the Ent Rate b/c I had a one night reservation at Carousel that required 4 days cancelation, otherwise they took a one night fee. HoJo added my night 3 days out! I was so bummed.
If you have a reservation directly through them and the good rate comes out, just call their 714 number during pacific time business hours (I recommend friending them on Facebook too...just the other day they updated their status to say that their In House people needed to take a half day, because they had training), ask for In House Reservations, and they will change your rate for you!