I don't know all of the rules to pre-op dieting, but to my understanding the reason we are to do this is so that our livers shrink, which makes it easier for the surgeon to perform the surgery. My surgeon said 1000 calories a day, suggested liquids but said that the only reason they suggest that is because it provides the nutrients you need and you don't have to worry about putting together a balanced 1000 calorie diet day to day.
I hope your meeting goes well, but I was given short notice for my surgery date, I had 2 weeks notice, and I lost 20lbs on 1000 calories a day, with exercise only a few times a week. Perhaps that is something your nutritionist can help you work out. Definitely keep moving, but try not to get discouraged because you're still losing!