Put a lot of heat on the I/O heatsink for about 10 minutes, I used a big propane torch, or until you see the thermal cement in the I/O heatsink melt and flow out on the pipe before you twist or pull on it.
Keep an eye in the slot where the pipe runs into the heatsink to look for the thermal glue melt.
The heat pipe is really thin and easy to destroy, so don't fatigue it by twisting on it too soon or handling the assembly roughly . . . .
Thanks for detailing it, will post here when I´ve tried it out!