Since my three sons travel around the state shooting the AR we built, to put my mind at ease .... I put a standard, rigid A2 stock on our gun.
Many people, in and out of NJ, pin the stocks themselves. Such as doing this ...
Some places such as Rock River Arms, sell "ASB Compliant" pinned stocks ... such as
http://www.rockriverarms.com/index.cfm?fuseaction=category.display&category_id=300
A north Jersey gunsmith I spoke with was hesitant to pin stocks because of the vagueness of the terminology of the law .... what actually makes the pinning
permanent? He didn't want to be responsible for his customers.
Good luck.
Jim