I'm using the hardware PWM output with wiringpi. It provides the function pwmSetClock that should make it possible to change the frequency. (https://projects.drogon.net/raspberry-pi/wiringpi/functions/). I believe since the default is 200 Mhz setting the divisor to 200000000 should make an LED hooked up to the output flash visibly, but that is not the case.
Can this be changed?