yes, I did it. With a 6,3 V Zener diode and a 1 K Ohm Poti, I built a 5,7 V power supply from the 12 V of the fan.
The laser is well regulated with the voltage from 0V to 5,7 V. I think , i will add a normal diode to get the voltage down to 5 V. I did some cutting test. The diode cuts Styrodur, 3 cm thickness, although the cut is wide (aprox. 2 mm)
It is a real power diode, so everything behind the styrodur gets burned. I have to take special precautions, otherwise I will burn my hobby room down.