OmegaDonut posted a method to do it, a long time ago, in the Help Thread of the RNG.
I can't tell you correctly in which page this happened, but I can say it happened on the last month, so you could start from there, searching for all OmegaDonut's posts on that thread on the last month, and you'll find it in no time.
Also, you'll have to choose beforehand which starter you want to abuse, if you want to abuse for shinyness.