Could you describe what you are eating for each of these meals? And when? Also how close to your workouts?
One good way to get use to 6 meals a day is to eat the same amount of calories, but split between 6 meals instead of your normal 4. (Example - 2000 calories divided by six would be 333 calories per meal.) Try to divide the time between meals as equally as possible, being sure to eat as soon as possible after getting up, and right before going to bed.
After you get use to eating like this, add 50 - 100 calories to the first, third, and fifth meals a couple times a week. Every once in a while add calories to the second, fourth, and sixth meals instead. Be more careful adding to those meals though. Keeping the even meals lower in calories might give you more time to digest, and not fill your stomach between the large meals.
I do find that my stomach does get use to extended changes in diet. After dieting I have trouble putting away normal sized meals, and after bulking it seems like a normal meal isn’t enough.
When I last bulked, I got a simple whey protein and mixed it with ice cream and milk to make a real protein shake. I also didn’t skimp on regular shakes either just to add calories. Ok maybe not exactly following a Berardi diet, but good if you have trouble getting enough calories.