You need to search for a spread with the IVs and Nature you want on RNG Reporter's Open Search that's exactly on the starter's initial frame. Then, you'll get the PID for that spread, and input that on Pandora's Box (there is a button inside RNG Reporter's initial screen) and search for ID/SID combinations that will make the spread shiny. Simple as that.
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.
Lol, it's no bother. I started this thread yesterday with pokes I've gotten through giveaways and such. I'm trying to build up my own stock so I don't have to rely so much on redis. pokes. Just takes more patience and making sure your pokes have the stats they need to function. The RNG'd pokes are intimidating, but I'm trying to make it up with good marketing and service.