Typically the issue isn't with the motion detector or the CFL, but with the photoresistor light sensor bundled with the motion detector to keep the light off during the day.
Step 1: What's being removed
Step 2: View of the circuit board on the back of the switch with the cover removed.
To fix the flicker the photoresistor needs to be removed. A photoresistor has a high resistance in the dark and a lower resistance the brighter it gets. Opening the junction will simulate complete darkness and always allow the light to turn on using the motion detector.
I didn't have a pair of cutters small enough to get to the sensor, so I used a pair of regular scissors.