You can disable the 45 degree camera lock in the game settings, however, you cannot tilt the camera or zoom out as far as you wish. That would have to be modded (or someone would have to find the setting that is responsible for this and edit it).
Be aware that the game is not supposed to have "over the shoulder"-esque 3rd person view or an adventure game 3rd person perspective since it has pretty aggressive culling and because some objects don't have a lower side since you don't see it anyway (=less rendering thus better performance). Some of these reasons are also responsible for the initial 45 degree lock. Take a look at the grass or bushes or a cliff that you can't see with the 45 degree lock and you'll know what I mean.
It just wasn't made for it and I assume that the good performance it has comes from the view and the aforementioned culling.
For mods, a free camera might be a neat addition though, especially once one can import own models and alike.
I get what you mean by the way, Neverwinter Nights allowed for this and it was nice, maybe even great, but from that perspective one could see the "optimization beauty issues". One of the things they should have done there for example is to add a fogring to the skybox with the same colour as the map's fog. The popping was awful! :P
