Hey there, Bryan, and welcome to planDisney!
As someone who is rather sensitive to smells, I completely empathize with your son’s plight and would be happy to help. While there isn’t a way to notate your specific request on your dining reservation, all hope is not lost. I suggest you reach out to the
Special Diets team at Special.Diets@DisneyWorld.com no sooner than 14 days prior to your arrival explaining your son’s particular needs in detail. Typically, they only deal with food allergy and special dietary requests, but there’s a good chance your son's needs would fall under the umbrella of what they can assist with. Once you send them an email, they will walk you through the next steps.
If, for some reason, they are not able to assist with your request, then I encourage you to arrive for your
dining reservations a little early to explain your son’s situation to the Cast Member at the check-in stand. They should be able to work with you, though you may have to wait a little longer to be seated to accommodate your request. Even if the Special Diets team can assist with your request, I still think it’s a good idea to remind the Cast Member at the check-in counter when you arrive to double-check your needs have been notated.
I hope this information proves useful, Bryan. Please stop back by if there is anything else we can do for you. Have a magical day!
See ya real soon,
Alyssa