been doing this for years, the way we handle it is to hide the element via javascript. then most screen readers won't "see" it, but generic form bots aren't that smart.

There are HTML attributes you can use to denote things like "ignore this field" for screen readers and the like.

http://www.w3.org/WAI/intro/aria

Adding a <label> saying "Do not fill this out, antispam filter" should probably be enough to mitigate that. (Disclaimer: I am lucky enough not to have to use screen readers etc.)

I think that it would be easily fixable. Every time you disable an account you send an email to the email address they registered letting them now about it with a link to reactivate it. For the reactivation, you can even add a normal catpcha to prevent the bots exploiting the loophole.