Personally, I don't think you have any disorder. Sounds like you just know what you want.
There are ways to achieve this permanently without making any clear physical changes. Just use the power of your brain to train yourself to have a limp little clitty.
Some ideas:
* Associate pain with an erection. If you get hard, apply pain to yourself (doesn't have to be your penis) until you get soft again.
* Masturbate HARD even when you aren't horny. Use a very strong grip.Think of it as "breaking your little clitty". Just abuse it until it cums while soft over and over again. Doing this 3 or more times a day will ensure you never have erections, especially strong ones.
* Only cum while your penis is soft. If it gets hard, stop masturbating and apply some pain to your body. This associates release with a nice, soft state which is becoming for a cuckold.
* Move your pleasure center from your penis to your ass. Use a dildo to milk yourself. Only allow yourself to cum with a toy rubbing your prostate.
For more methods, search Limp Clitty Training.