I had to do MediFast for two weeks prior to surgery the first three days were brutal...after that it was pretty easy sailing. From what I understand, and I'm no doctor, it's not just about shrinking the liver it's about how much room ends up around there because of it's size meaning less air has to be put in...for instance, I did the diet and had literally no gas pain except for the first night.
MORE IMPORTANTLY, in those two weeks and the week after surgery I lost 27 lbs and it gave me a huge morale boost...so do the diet and you'll get a fantastic mental jump start.