I have just watched the movie recently and I'm not sure there's enough music for a 2 CD release. Yes, the original album is quite short but there's not much music missing. The only way to fill a CD with enough additional score is to contain suites or early ideas and demos like on other Zimmer CDs. That would be great.
There is literally so much music missing on that album.
I just saw the film yesterday and absolutely love it! It's one of my all time favorite films, and easily my favorite of the year. I hope it gets a Best Picture Oscar nomination.