I have been working on this and have a half-baked solution - although not by any means acceptable.
Since the DAO_PRC_EP_1 file is missing - I went to the Documents/Bioware/Dragon Age/AddIns folder to see that indeed that file was not there. To try to fix this, I went to the Dragon Age Origins Awakening Installer and right clicked on that, and selected "Show Package Contents" then "Contents" then "Resources" then "Awakening.tgz" which takes a little while to expand because I believe this contains most of the expansion. I then moved the "DAO_PRC_EP_1" file into the Documents/Bioware/Dragon Age/AddIns folder where i believe most of the rest of the DLC is located.
After this, I could access the game finally!! However lots of animation was missing, the blood dragon armor dlc was missing, but i was at least able to see some of the opening animation and play some of the game, albeit with missing portraits, and some other wonky things like awarding 210 exp for killing low level darkspawn.
Based on all of this, it leads me to conclude that the install is totally bogus, at least for us, and it is not actually installing or doing a complete install.
Thus, I think the solution may rest in somehow being able to do a full, manual install on the mac. The question I would pose - and I am certain must be doable - is how do you do this??