I've been trying to. The giant pull requests are his own self-inflicted pain. He'll massively expand the scope of the original ticket -- or does everything all at once rather than one piece at a time. It's something we talked about, again, on Thursday because his current ticket was supposed to be a quick 1-day thing that's now 2+ weeks. The additions are good ideas, but easily should have been their own tickets/done afterwards.
(I was on vacation when he was assigned the task; it's too late to course correct)
That's the struggle? He's in a weird space where he's capable of prototyping solutions/things, but are problematic long term.
We're a really small team, so it's hard to justify pushing him towards alternatives like writing tests/docs. I would love to get more automated testing though, maybe I'll revisit the topic.