Simple, they're still evil, but less evil, by making them a place to do therapy like stuff.

One ankle exercise that helps with balance that people are taught to do if they sprain ankles is to just raise up on their toes and then go back down, and repeat this. If its to help with an ankle injury its generally done on one foot.

However, I've found, if you do this standing on both feet, while washing, then what it does is:
1. Give you propioceptive input.
2. Give you a particular sort of vestibular input.
3. Give you vestibular challenging to work on helping train your ability to balance (making it easier to balance in the long run by practicing in a situation that's just a little too hard)
4. Make you practice with crossing the midline (a thing that would be overlooked I think, but very clear from my tests)
5. Make you practice with identifying finding moving body parts.
6. Work on strengthening your legs and core; good for anyone with motor disorders, or with issues with balance, as core weakening tends to eventually come from too much issues with the vestibular sense even if it wasn't there originally

To increase the challenge, while washing one leg, just continue on the other leg. I am not capable of that at all. I also stop when washing my face, I cannot do the motor planning to understand where my face is when its moving even if my hands are moving at the same time.

To decrease the challenge, use an elbow, or a hand (if you have a way to do that without issues with soap) to balance against a wall. Just placing it against the wall lightly helps a lot with balance generally, and doing that at first isn't a problem. I actually leaned against the wall to wash one leg because this caused me to have issues balancing on one leg even while I wasn't moving, but standing on both legs I was fine. Depends on what your abilities are.

10 seconds of not doing this while showering and I'm nauseous. Do this and I can hold off the overload. My legs might hurt, but exercise pain is better than nausea.

Now I just need to figure out how to not want to chew my hands off, because now I really want to chew my hands off. I hate showers so much.

You really have my sympathies. I love your idea. Have you tried brushing your skin before you go in. I recently discovered I could change the way the water came down. I turned it into short bursts and that seems to work. You will need to have an attachment on the faucet for this. My other trick is to limit the amount of time the water is on you.You can get soaked in a few seconds.Or maby you can soap up using the sensory brushes with soap! I bet that would feel great. I now wanna get sensory brushes just for that purpose. Showers can be quite nice if it is done right. I also wonder if aroma therapy can make it more nice. I think I am going to try using a washcloth in soothing motions on my skin.Soft towels are a must although I can take rough towels. Good luck.Hopefully you will get the torture to end.

I found this thread through a link on an SPD article that the DBSA shared on facebook...
I have this HUGE aversion to showers and getting wet in general, but when I actually make myself shower, I don't enjoy it but I don't have any physical pain or sickness or anything.. I don't like the feeling of water and even more I HATE the feeling of being wet when I get out of the shower...
It has affected two different jobs because I have such an intense anxiety related to showering that I shower twice a week at best, and I've had two different jobs talk to me about hygiene...

Do any of you experience similar? Or is it like the sensation of water hitting you that drives you nuts? Is it different for everyone?

Pretty much everything to do with showering is a huge problem for me. It's one of the areas we measured success in in OT actually.

I get nauseous. I lose my balance. I have lost vision. I've actually almost hit the ground uncontrollably before. I have vomited before. I can't figure out when the soap is off my face. The wet bothers me after. Drying off bothers me more. Fabric touching me when I'm wet bothers me even more. Every last thing touching me, including air, bothers me, after a shower.

The wrong sorts of drips feel wrong. It makes my body hurt more. But at the same time, I crave water badly, and its the best way to get heat into my body. Balancing the craving and the overwhelming of a shower is even harder in some ways I find. I LOVE water. But I hate showers. They're terrible horrible things.

I am actually typing this up to avoid a shower currently...

I wrote up before a description of a shower. http://turtleisaverb.blogspot.com/2014/02/a-shower.html

That's generally what showering is like for me.