Yes, I booked diniing with a 40% PIN code....once a CM allowed me to! On my first two calls to make or change ressies, the CMs told me I could have the 40% off on a room only ressie or a package with MYW tix, dining,e tc., not both.
I was thrilled when I called a third (or was it fourth?

) time, and the CM asked if I knew I could make it into a package. I guess it's possible that the rules on the PIN changed at some point, my first few calls were *right* after I got the pin postcard.... Anyway, I made it into a 4 nt package with dining, and later to the date I'll add a room only ressie on the PIN code for one or two nights at the end (to make it easier to use up all our credits on the last day, and get a lift back to MCO -- even if we don't spend our last 2 days at WDW, it's still a bargain.)
The only frustrating part for me is that DH is *not* keen on WDW at all, and he's dithering about whether he wants to go. He *does* like nice hotels, and only needs an internet connection for work, so I've floated the idea of him coming with, and my whisking the girls away to the parks while he sleeps in, works, and joins us for a few hours here and there. We'll see.
I'm not keen on going every year, but I don't know when we'll be able to bring ourselves to pay for 4 nights in deluxe, let alone book at a rate which essentially makes our dining free adn the tickets half price! The December dates start right after our 'birthday week' here -- DDs and DHs all have early Dec birthdays, and I'm not sure how long we'll be comfortable with hauling them out of school for off-peak trips (They'll be in kindergarten, so no problem this year....)
Long story short? If you get a CM who won't let you build a package with a PIN, it may be worth calling back later and double checking.