Maybe a spiral band like these? I personally love these little things, one of my kids got a bracelet like these in a goodie bag and I use it to fidget.
https://www.amazon.com/dp/B07MT8T1C2/ref=cm_sw_r_sms_api_i_SudmFb...
Although it's a little harsh, it's the only soap I'll ever use.
I can't stand soap with scents, etc. Maybe your soap makes him really itchy.
If you like to research, look up misophonia - the term for what you are experiencing. I have recently found earplugs that can silence really annoying noises while still allowing me to hear people talking to me or the TV or whatever.
DownBeats Reusable High Fidelity... https://www.amazon.com/dp/B00A3Z44R2?ref=ppx_pop_mob_ap_share
Ask them what stink they're trying to cover up? That's all I can think in scented houses, like what nasty are you covering? Lol
I hate scents, too. I found an air freshener gel that works by removing stinks rather than adding extra crap to the air. It has a light natural scent that is barely noticeable. Maybe they'd be willing to switch to it? It's fabulous and does what it should. Fresh Wave Odor Removing Gel, 15 oz. (Pack of 2) https://www.amazon.com/dp/B000I9QJ5S/ref=cm_sw_r_apan_glt_fabc_15BSGVR080JF142N31C1
There's a few sizes and refill jugs, too.
If they say they like the smell then maybe you can see if they'll just use it in their room and not the common areas. Fingers crossed for you!
In a lot of groups I'm in autistic adults are recommending this one instead: The Awesome Autistic Go-Guide For Teens and Tweens
https://www.amazon.com/Awesome-Autistic-Go-Guide-Practical/dp/1787753166
Asperger's is outdated language now that it's no longer diagnosed.