The 'pumping the collective' method is more or less, getting the rotor system ahead of the governor (if installed). If you have exhausted your lower RRPM limits, or you have little or no RRPM range (in training; real emergency-what limit?), and you still find yourself turning left...
Your series of quick pulls will overpitch the machine essentially, RRPM will drop, altitude will increase and the guv will say "Wow that was fast! Heres some torque" As the nose rotates around, you quicky lower the pole, but the governor is still pouring on that last bit of torque (now excess torque, as you've flattened pitch very quicky). You will find yourself straight for a moment. Ground comes rushing up, pull again. Repeat.
By experimenting with how fast and hard you have to pump the collective, you can keep it straight and eventually work yourself lower and lower to touchdown.