I am going to say something that is opposite.
If you are going to go into this surgery go into it 100%
Why wait until 85% of your stomach is out to work on you? Aren't you worth more than that. Spending your time pre-surgery gaining weight is not the right way to go into such a very restrictive surgery. All surgeries carry risks, why not do your best before surgery to limit the risks by taking care of yourself.
Start charting your food on something like myfitnesspal.com Start trying to lower your carb intake now. I put myself on 800-1000 calories a day (I usually stayed around 800 calories and on my "fore-special days" where I went out to eat at Red Lobster or a Japanese Steakhouse - I went higher. I made sure I kept my carbs 45-75 ...unless it was a fore-special day, which I only did once a month or maybe twice a month.
I lost 10 pounds a month during my pre-approval phase. I got to have my favorite foods once in a while, but I also learned to break the bad patterns that you will need to break eventually, if you don't break it pre-surgery, well who says you are going to be able to break if after surgery?
Learn to not drink with your meal and wait 1/2 hour after you eat to drink your water. Chart your 64 ounces of water a day, chart your exercise. Learn how to do this now.
Limit your caffeine until you can go off it completely (imagine weaning from caffeine and carbonation during pre-op shake....) people that do it before pre-op shake are more successful.
If you are going to have Last Suppers, or Last meals before pre-op shake don't do it the day before do it days before because carb overload, will make pre-op shakes so much worse.
Nobody said you have to starve yourself, but why gain weight? Wouldn't it be nicer to have less to lose after surgery?
It sure was for me. Even if you lose 10 pounds or 5 pounds pre-surgery isn't that something to be proud of? Aren't you worth putting 100% effort into this?
The food issues you have pre-surgery, the comfort food, or the love for food don't disappear after they take 85% of your stomach. You are still going to have stress, you are still going to have anxiety, you are still going to need comfort. I guarantee you, if you work on these issues before surgery and put effort into this, you will be more successful after surgery, because the surgery doesn't cure what caused you to become overweight to begin with.
This is not meant to put anyone down, this is not meant to hurt anyone's feelings, but this costs a whole lot of money and this surgery is NOT a walk in the park. It takes hard work and dedication and it will not solve your problems if you don't work hard for it.
Best of luck to you all.