Spirex,
Recent NJ court rulings allow the possession of full capacity magazines, as long as they are blocked down to no more than 15 rounds. This may to done by any means, either temporary or permanent. Even empty shell casing may even be used.
I would pull off the base plate, and insert a wood dowel. Just make sure that the dowel is long enough to block them well below 15 rounds. The person receiving the mags can fine tune the capacity once they receive them.
The way I read the law, it is the "possession" of full capacity mags that is illegal, so the one receiving them is taking most of the risk.
Oh, one last thing - "Pet Peeve Alert On"! Let's not use the inaccurate phrases created by the Antis. Pre-band mags are "standard" or "full" capacity, not "high" capacity. Post band mags should be referred to as "reduced" capacity, or "gilded" mags. "Pet Peeve Alert Off"