I agree with Mark.
Free verse sonnet is - as has already been mentioned - a contradiction in terms. What is it? A sonnet or free verse? It's either one, but can't be both.
Sure, free verse can contain sonnet-like qualities. Or other form aspects. But that doesn't make it a sonnet, which is a strict form. After all, the essence of free verse is that it's not restricted by form - even if it incorporates elements of form, it's still not restricted by it. The moment that happens, the boundary between free verse and form poetry is crossed and the work in question becomes a (traditional) form verse.
To me, it's more or less like how a man cannot be a woman or a woman a man, even though they can be androgynous. For the sake of the argument, let's presume I look like a guy, walk like a guy, talk like one and fancy women over men. That still doesn't make me a man. Or a man-woman, or whatever. I'd (most likely) be a cross-dresser and (obviously) a dyke. But still a woman.
However, the moment I had surgery - yes, the kind that removed my female assets and gave me male parts, I could argue that I were a man. I wouldn't be recogniseable as a woman anymore, not even naked. (Still... there'd be some room left for argument, as my DNA would still be the DNA of a female - but that's nitpicking and not related to the discussion we're having here.)
Back to poetry:
Free verse can contain elements of form. It can contain many elements of form. However, the moment you doctor it to such a degree that it's recogniseable as a particular form, it's a form verse.