I didn't tried this ORAS hack yet, but these steps worked with me so far, for Pokémon Neo Y and CTGP-7 (Mario Kart 7 mod). I changed the instructions from the looks of this ORAS mod download pack:
1) Before everything, open your game through HANS and mark their titleid.
2) Dump your game with BrainDumps
3) Download the PackHack kit, available here: http://pastebin.com/A1s8cmsD
4) Extract it, open RomFS Extractor and choose your romfs.bin dumped from your original game. A folder named romfs_ should appear at the end
5) Download this ORAS pack according to your desired game, extract it. Look for the folder "a" inside the "romfs" folder. Copy the "a" folder
6) Now open the "romfs_" generated on Step 4, and paste the "a" folder. When you're asked to overwrite files, say "Yes".
7) After that, open the PackHack kit again, open the RomFS Builder, and repack the "romfs_" folder. At the end, you will be asked to save this file: use the format "titleid.romfs" for saving this file.
8) Now, open HxD ( http://mh-nexus.de/en/hxd/ ). Select the Hex bytes since the beginning, until the 0xFFF line (doing that, you will see the number "1000" on the foot of the program. Click to enlarge this example pic)
9) Delete these selected Hex bytes, then save.
10) Place this edited titleid.romfs on the "hans" folder on your SD Card, boot the 3DS, then HANS through HBL.
11) Just set the ROMFS option to "Yes", then boot your game.
It should work.