Okay, I finally found the info. It's from a UK mag called Cycling Plus, the March 2007 edition:

"Starting with the basics, you have two choices of fuel; carbohydrate and fat. Carbs provide around 1500 to 2000 calories when muscles are fully 'carb loaded'. This higher octane fuel can help you go long when combined with fat use or can fuel quick efforts/sustained high-intensity riding on its own.
The fat stored under your skin and within muscles themselves is a very high-calorie fuel depot. Even lean riders like Lance Armstrong had over 30,000 calories stored as fat. Fat use generally increases steadily as a ride draws out, starting with the use of fat droplets stored in muscle and then gradually using fat circulating in the blood stream that is coming off the 'chub' stores spread around the body. Even during long training rides you will still be using carbs. The secret is to keep ride intensity under 80% of your max heart rate and ride for long periods.

Do not underestimate the importance of food. What you eat before, during and after riding does affect your fat burning capabilities. Feeding carbs before and during a 2 hour ride significantly decreases the use of fats stored within muscle fibres."

Then it goes on with the recommendation I tried on Saturday morning (which, for me, did not work).