I swear they nerfed him. Nobody should need to cheese him at all. It was rare that he was summoning any adds, probably 3 skeletons after a dozen throws.

If it is really just for fun...
* Perhaps build a dome and have him walk over campfires?. Perhaps around pyres.
* Park him over a flame-creature spawn. LOL, that melts the Abominations (trees) also.

The dome would work easier in your... dirt wall. I assume bosses break stuff nearby from summoning. They really really really need their own phase/instance where players can't cheese them and they can function ... even normally. Moder is HORRIBLE. Yag can get stuck (my actual first experience)

I've walked a Lox around a pyre before. It was just stupid silly. The deer will run away, but at these creatures give no care about burning to death.