No More Erections by Senna might work for you. I've never used it, but folks have given it high ratings. The author claims that it will render the listener incapable of getting erections indefinitely. As with all hypnosis files, it probably will take repeated listening, from a week up to several months, depending on how easily you trance, to work.
If that doesn't work for you there might be others in the free section, and if not, you could always pay EMG for a custom file along these lines, if you have/want to spend the cash.
Send me a PM if I can help in any way.
Good luck!