there are many reasons this has not been done the main being the ban hammer!! it would be hex editing in the game save, you would first need to locate it, then you cant just delete it, you would have to change it to a like code. then rehash, resign and all the lovely mess that goes along with it. mybe not imposible, but definatly not practical, even if you did get it done, I would emagine it would not take MS long find you, there is a diference between modding hardware you own, and modifying leased software, that you technically dont own.
good luck with that.
buy a chip, there are three good ones I know of, hazer, viking, and act.