Also he uses VPN/proxy or Tor has some glitch on clearnet that can be exploited but which I can't safely reproduce.
If one of you could experiment with Tor on clearnet and report his findings that could help.
What I suspect he opens endchan.org or .net on Tor with JS enabled or disabled (have to test all), and posts from one until he gets banned then he recycles.
In theory this shouldn't work, but perhaps it's do somehow.

I don't think he posts on his home/tel IP anymore.
Also there is a lot IPs in one thread with only a handful of post. Only a few IPs/ranges rack up lots of posts.