The "Alternate Ending" is achieved when you do NOT press space to open the door after Salvadore cut off the power in the prison. After a while the door will close again, and you will receive letters from Dr. Money.
The Letters (spoiler alert): Edit
"You made a wise choice. Now you get to enjoy your freedom to play all the games on your entertainment system you want. Congratulations, you imbecile."
"Do you know why you were locked up here?, You're So Stupid."
"Of course you are aware of your innocence."
"You know organs are slim now because the virus I created destroyed them. Working organs go for a lot of money these days."
"There is nothing more that people value more than their own survival. It doesn't matter how poor the quality of the organs I'm supplying is, they keep coming back to me."
"But the real money lies in selling high quality organs. Especially if they come from people who are immune to the virus."
"People like you."
"Remember the shot you received when you arrived in this prison?"
"It was the only working antidote."
"You are worth millions now."
"That is, your organs."
"I made you relevant. You should be thanking me."
"You are one of the few people I chose to be immune."
"You are one of the few people I locked up."
"And your organs will be the world's most sought-after resource."
"Thank you for your cooperation."
"You will be hearing from us shortly."
End Text: Edit
Your life lasted 12 more days.
In that time, you managed to complete all of the games on your portable entertainment product. Yes. Even Crankmaster.
You realized that you were all alone.
You heard footsteps approaching.
You saw your cell door open slowly.
You couldn't make out the face of the man who entered your cell.