You can, but not as easily. The CPU clock is achieved by multiplying the base clock by its internal multiplier. K version CPUs can change their multiplier, making overclock very straightforward. Non-K CPUs can't change their multiplier, so overclock must be done by increasing the base clock.
The problem with messing with the base clock is that it also changes frequency for other controllers, such as memory. It is very hard to achieve a decent overclock by changing the base clock, because the motherboard will most certainly have issues.