Not at elite 4 arons door, but in jublelife.
Use the tweaking glitch to get inside the olace the gives you poketech apps. Not were it displays what's inside.
Walk to the entranse(after you open the pokedex) from the back.
And you'll come out in the void.
Here is a ivdeo with the rest of the instructions:
You can only get out if you fly away once your in newmoon island or you use an escape rope while your in the turnback cave part.
You can't get on the land.
Evan after you go to canalave.
There's no option to sail there.