looking for a sims 3 code for use on exchange

A friend of mine gave me his old copy of The Sims 3 since he wasn't playing it any more. The game works fine, but I when I went on the Exchange to download custom content, it said I had to register my game to do so. When I tried to do that, it said the product key was invalid (probably because he had it registered under his name). Would anyone who does not use The Exchange be willing to let me register their product key so I can download custom content? If not, is there a way around this or should I just give up on being able to do so?