What @techmom99 ^said. I think that there are a lot more adults that have this condition than people realize. I imagine colleges have dealt with it before. Contact the school’s disability/access services office and present the problem to them with documentation along with the fact that it is associated with ADHD. I would imagine they would be required to keep this info confidential and would provide them an accommodation of a single room and then other accommodations for the ADHD if necessary. This would also allow him special accommodations for any required overnight field trips that might be required in his field of study (I had a couple of required overnight field trips and an 8 week “summer camp” (8 credits of classes that had to be completed in an outdoor environment and the students stayed in multi-person cabins).
And no, do not disclose the condition to the guidance counselor, address it on the Common App, or discuss it with anyone other than the disability services office. It is no one’s business, especially the admissions staff, and it has nothing to do with his EC’s.
You’ve stated that your son would be upset if you disclosed this to the school, but how does he expect to deal with the situation unless you do? The only way I can think of him going to college without having to disclose the info is if he commuted, got off campus housing with his own room, or he applied to schools where students are able to get single rooms for an additional fee and that enough single rooms are available to everyone who requests one. I would think those colleges would be rare, but maybe you could do some research to see if there are any that are a good fit for him and your family.
Good luck.