Hello, I am a psychiatrist.
I guess it might depend on your end goal.
If your end goal in talking to him more about it is to just let him no that you support him all the way and love him no less at all, then that can probably be communicated either indirectly or directly. If he sees that over time you don't act the smallest bit different towards him, that you have unconditional acceptance towards him, then he may come to realize that without your ever saying anything else to him. At the same time, you know him, and it might be that initially he'd be uncomfortable about your bringing it up again, but then really appreciate it after the fact. I cannot comment on which approach to use, not knowing him.
However, in case he is not aware that there is effective treatment for Tourette's Syndrome, telling him that there is may give him some hope that he can be rid of the symptoms of Tourette's (or some of them). This is something that needs to be investigated cautiously, though, in terms of his medical certificate for his commercial pilot's license; it is possible that treatment would be a non-issue, but some of the medications used to treat Tourette's might be viewed as unacceptable for him to take either while flying, or while holding a commercial pilot's license. The best thing to do would be to contact an FAA medical examiner anonymously, and see what you can find out. If there is no issue with having Tourette's and/or being treated for it while flying or even having his commercial license, then it is possible that he could be freed of the symptoms that have caused him so much shame and distress.
An aviation medical examiner can be found here:http://www.faa.gov/pilots/amelocator/
Does this make sense?