In the end I had to halter Luc and show him the old fashioned way, saying, "Hey, look at this really important thing, and don't be afraid." Which isn't nearly as fun as learning about it by himself.
It feels good to be doing some actual training again, rather than just letting him integrate into the routine and learn to be a domestic horse. I think this extra time to settle has been good for his emotional well-being, but we all have to go to school at some point. Soon we'll be swinging the saddle up.
I still have no plans to ride him this year. Note how little he is in the picture next to Scout. I hope he grows, but if he doesn't, he will at least mature.