I replaced about 4-8 shoulders that way, it is great to add/reduce musicians, standards, lances, and preceptors. I use a 1/4" rare earth magnet on the shoulder socket and in the shoulder torso. Drilling it out is pretty easy, just do a 1/8" prep hole to guide it in smoothly.
One thing to always check before you glue is the polarity. Ensure you do all of the torsos the same way and all of the arms the same way, otherwise you will end up with arms that are repelled from the magnet.