Thank you…
You are right... didn't notice that expansion headers heater pins could be reserved for something else with M307...
I think I will use the M42 for my purpose... should be rather easy to implement on post processor...
So to summarize best course of action is:
1. First disable expansion header heaters with M307
2. Then you can use M42 for driving them.
3. For 5V Pwm it's easiest to use 3.3V -> 5V Logic level converter as interface https://www.sparkfun.com/products/12009