Hello and welcome,
My advice... follow doctors orders when it comes to the pre-op diet. This is a great time to get a jump start on losing those pounds. It will be over before you know it. A trick that helped me make the pre-op stage was. Protein shake, mix with lots of crushed ice and milk, add 1/2 packet of sugar free pudding powder and mix well. This is great and fills you up to the brim. You also get the feeling that you treated yourself to some delicious ice cream. I loved Vanilla Protein Shake Powder, Milk and sugar free Butterscotch Pudding Powder. The mood lifted and I still lost those 16 lbs before surgery.
Good luck.