Here in Minnesota you can register vehicles at any of the "license bureaus" or Deputy Registrars.
The problem is that most of them, especially the ones in the larger communities, will most likely catch that the motorcycle is really a dirt bike and they usually won't let you register it.
I've found that if you find a very, very, very, rural Deputy Registrar's office, one thats far away from the bigger cities that isn't paying attention to all of the details and paperwork you provided, they most likely will let you register just about anything as long as they don't see "for off-road use" anywhere on the MSO.
Once you have it registered (at the Deputy Registrars office) cross your fingers that the State of Minnesota doesn't catch it when they process the paper work to issue you a title as the VIN numbers often indicate that the vehicle started life as an off-road motorycle.
If you're lucky you get a Minnesota title in the mail about 30 days later.