After much searching here and on the web and in developer forums, I can\'t believe that nobody seems to have even asked this question before.
The iOS autocorrect sug
The UITextInput
protocol defines a method - (NSDictionary *)textStylingAtPosition:(UITextPosition *)position inDirection:(UITextStorageDirection)direction
which the docs claim can be used to style correction rectangles. I gather this would be communicated through a UITextPosition subclass that indicates styling information is being requested, but I'm not sure on the details of that. Something to look more into for sure!
EDIT:
I just implemented a UITextField and a UITextView subclass and overrode the below method. The method was never called :( Sorry to answer with false hope!
EDIT 2: found a blog post explaining why it was never called: http://bjhomer.blogspot.com/2011/11/detecting-backspace-in-uitextfield.html