Note: This answer only applies specifically for the input form (I misunderstood the question above)
I was able to accomplish this by using simply modifying the entityform made configuration.
- Go to /admin/structure/entityform_types
- Click on the edit link for the entity form you wish to change
- Scroll to the bottom and in the URL path settings set the specific custom paths that you wish
- Save
It's that easy and it works for both the preview and the actual form :)