This is pretty much unknown, but it does exist (it got linked on an old forum thread on here), and I plan to use it for a FiM fanmade episode thing I'm trying to start, but Hasbro does have a "Permission to Use" request/form system.
So if you want to try this route, you can, and I'll leave the links to it.
A bit of instructions under the "Permission to Use" drop-down: http://newsroom.hasbro.com/contact-us
And the form one would need to submit: https://corporate.hasbro.com/documents/Hasbro-Permission-to-Use-request-Form.pdf
Mind you this is no guarantee you'll get permission, but this would be the least dodgy way going about what you're trying (if you wanna make money, and if you don't, it's still a good idea).