How to hold back hunger for a very long time to get ketones?

Several options. Drink a lot of water and take fiber capsules to keep you full. Look into l-glutamine and l-tyrosine supplements (these are amino acids). Also, you don't have to stay hungry to start ketosis. U just have to eat very low carbs. So when hungry, eat meat, eggs, cheese, non-starchy veggies. No grains or sugar or potatoes or corn or fruit.