For anyone that needs help getting Epona in the first stable slot:
Set your Wii U up for the trainer.
Instead of using the trainer use JGecko U.
Click add code, name it whatever youd like, insert the Epona code:
01000038 4011EBD4
47616D65 526F6D48
6F727365 45706F6E
61000000 00000000
press...