It's called a "living trust", they are most commonly used to avoid paying death taxes and going through probate. They are similar to a corporation, a "legal person" that can own property. Real flesh and blood people are known as "natural persons" in legalese. Normally all it takes is filing some paperwork with your state to set one up, a lawyer is definitely recommended although some Will writing software includes trust setup forms.
The requirement for a local LE "signoff" is the major stumbling block to NFA ownership for most people. If your local chief or sheriff doesn't want to approve youir application going the trust or corp route cuts him out of the process.
In a traditional living trust situation the person transfers all their assets to it and names their heirs as in line to control the trust after their death. Thus, when they die no will or probate needs to be processed, the control of the trust automatically transfers to the next person in line.
In regards to NFA items the trust or corporation can own property including NFA items. Since a "legal person" can't have a police record the trust or corp does not have to get the permission of local law enforcement to own NFA items.