Telling him "That's OK ... you can be a girl and get your parts chopped off and have plastic boobs installed" won't fix things either. Still, the real problem isn't the kid (who mainly is just a nut); the real problem is the supposed adults who pander to his sick delusions and perverted fantasies.
At this point, the kid can’t just be ignored.
No matter where he goes now, people will know.
Something has to be done, and I think providing a restroom near the administration offices would be a good resolution to the matter.
Let the gender benders co-mingle there.
So who’s going going to be there to represent the millions of young girls who will be forced to undress and shower with some dude or dudes who use the rule to claim they are female arrghh it’s just sick.