Is there a rule, in the Mary's room argument, against Mary doing some brain/electricity experiments on herself? Of course, she would be careful to use non-red tools and change her blood somehow so it isn't red either.
I would expect that such a capable scientist could learn what it feels like to see red objects without any red light going through her eyeballs.
Unless I am mistaken, ESR either thinks that these experiments are not allowed, or hasn't thought of that possibility. This makes me believe that ESR's idea that he disagrees with Dennett might be based on reasoning from different ground rules than Dennett.
Funny how those highly unlikely borderline cases whisk away a lot of the confusion, huh? No committed physicalist can postulate a serious difference between seeing something red and having a virtual red-thing pumped into your optic nerve, I would hope. I think that’s a far more useful scenario than thinking about someone suddenly be able to see colour. In fact, you could probably keep moving a step towards your magical ‘inner perceiver’ and asking whether ‘it’s a real experience of redness’. That’s not to say that qualia are fundamentally dualistic, simply...
http://esr.ibiblio.org/?p=1192#more-1192
ADDED: Even if you disagree with ESR's take, and many will, this is the clearest definition I have seen on what qualia is. So it should present a useful starting point, even for those who strongly disagree, to argue from.