Calm down everyone. Let's breakdown Scott's reply:
The ONLY way to do away with the Automatic Reduction of Fill Flash on the 1D Mark II and 20D is by putting the Camera's metering mode to Manual.
This is the answer to the original question.
This is where additional information and/or a more comprehensive explanation may be found.
It pays to read the whole thread.
I guess this is where there's some misunderstanding. Apparently, the link above is a very long thread with information dispersed throughout the whole of it. Hence, the recommendation to "read the whole thread".
I suppose the above statement would be negative if you had previously been directed to that link and then returned without finding the answer. Then, the interpretation would be like "the answer is there, you just didn't read the whole thread". This is not the case though. The answer has already been provided. The link is just a bonus.