It's all food and water.
Eat around 3000 calories of carb based junk food at around 11 am. Consume 2 litres of water at this time.
Go to sleep. Wake up later in the day, drink as much water as possible.
By 6pm ur glycogen stores will be full, pushing the hard muscle against the skin.
I will endorse this statement

the night before i took this pic, this is what i ate
2 pints of Ben and Jerry's ice cream
1 giant Nestle crunch bar
1 whole bag of Pepperidge farm oatmeal cookies
2 bags of Peanut M and M's
1 regular snickers bar
the morning after, I did a pretty hardcore "marathon " type work out involving kettlebells, pull ups, stair running, FULL sit ups and burpees
this pic was taken at 500pm btw