Except I'd like to do it healthily.
Sumo-wrestlers actually eat a very healthy diet to gain weight: They eat Chanko-nabe; This is a type of stew and contains large quantities of protein sources such as chicken, fish and tofu as well as masses of vegatable and vegetable which contain huge amounts of calories.
They also follow these other steps:
Skipping breakfast
This may seem illogical in respect to gaining weight, however according to Dr. Wayne Callaway, obesity specialist at George Washington University, skipping breakfast can not only trigger overeating later in the day but can also cause a drop in metabolism. It was found in research that people who do have breakfast, like sumo wrestlers have a five-percent lower metabolism than those who don't skip breakfast. This is because by comsuming calories, our body uses more energy to digest and absorb the food.
Drinking beer with meals
With some beers containing over 200 calories per pint, consuming it with food helps sumo wrestlers to gain even more calories. Sumo wrestlers will easily consume 6 pints of beer per meal. Alcholic drinks are known to be 'empty calories', meaning that they have absolutely no nutritional value except for providing energy, which means that it will be stored as fat.
Exercising on an empty stomach
Although exercise does increase metabolism, exercising on an empty stomach will infact lower your metabolic rate in the long term. This is because your body tries to conserve as much fuel as possible by rationing what's available.
Have a sociable meal
Researchers have found that by eating with others and socializing we tend to consume more food because it takes us longer to get full. As sumo wrestlers are literally stuffing their stomachs to their limit with each meal, the more food and calories they intake, the more fat will be stored.
Having a nap after lunch
Sumo wrestlers commonly sleep for four hours immediately after lunch. As mentioned, this allows more of the calories to be taken on and stored as fat in the body rather than being used as energy.
They gain weight while REMAINING healthy; It has to be done very carefully.