The hack first showed up over on the forums of fansite On-Mirror's-Edge. As developer DICE designed the game for the first-person view, the model for Faith isn't properly animated and the camera can't be moved up or down, but the game is playable.
Directions for the hack, which requires editing the TDInput file, follow below:
go to "DocumentsEA GamesMirror's EdgeTdGameConfig"
open the file "TDInput" with notepad.
add this line to the "bindings" list:
press F4 a few times. first you get the free cam (noclip) and later the third person cam.
Thanks to YouTube's jbdvrock for the video.