Gamespot just posted an article about this in there news section: easy guess what the comments are like 
Never has there been a more wretched hive of scum and villainy!
So the only way to get extra paid for characters would either to have the files in the game and accessed when the DLC is paid for, an expansion pack like Awakenings, DLC where the extra character is only available for it instead of the entire game, or just to do like Bioware did with Zaeed and Kasumi and limit the real dialogue to the missions (the only downside of those two characters).
Out of all of those I think having the files in the game and accessed when the DLC is paid for would be the best option to have a real fleshed out character but then we'd have another Crusade against Day 1 DLC (which is why we can't have nice things.).
Oh and here's a link to the Gamespot article:
http://www.gamespot....y/1100-6418895/