Interact with DC on his stream. Give some ideas or just chat casually. And if DC finds you interesting enough and you are interacting with him for a while he might add you to the game. Sometimes he does a raffle on his stream for new characters too, So people can propose ideas for the character.Say, do you guys know how did people got to introducfe their own characters into the game?
I can't say this is 100% the right way but this is how it's happening there for the 3 years I have been watching his stream.
(Sorry for my English if there are any mistakes.)