Practically speaking (read: as far as you, I and the rest of the world are concerned), no it is not possible. Apple has chosen to solder the CPUs in their notebooks for some time, rather than using a socket for them like most computers (including most notebooks) do. This serves two purposes for Apple; one, it ensures that end users are forced to buy a new machine rather than upgrade their existing one (which makes the bean counters very happy indeed), and two, it reduces the overall height of the processor by a bit, which allows them to make the notebook a little bit thinner.