If you could figure out which tiny little parts to move, it may be possible. However, they process of overclocking in this way could easily result in a destroyed PB. Even if you did it, pushing the CPU very hard at all could result in overheating, cooking your PB. It would most definitely not be covered under warranty. Don't bother with it.
Somebody sells CPU upgrades for those, but they are quite expensive. My call is: don't bother. Looking at the specs in your sig, the only way to go faster would be a 7200-RPM HDD.