That’s what I decided in the last 24h reading the aforementioned thread again and again.
Though the copper rod is not just for filling space, but essential for heat sinking to.
I’m lacking tools, so I would like to try this mod using only a soldering iron and a dremel tool (for polishing the copper rod).
I would buy the copper locally, there are companies doing the cutting and milling for you.
(Would cost ~10€ for one heat sink of 22mm diameter, 20mm length and a 3mm hole drilled.)
I found this thread of dorpmuller very inspiring too:
I would probably go with a mix of both threads.
Plus I think that P60 lights are still usable, because there are many successful mods out there, wether it be Surefire, Solarforce or custom lights.