Ben, don’t know about plastic tweezers, but how about small wooden tongs, like the kind you use in the kitchen to pull toast?? Depends on how big the tongs are and how tight the clearance is between the magnet and the arm socket. The other thing I use to reach pieces that fall in hard to reach places is to put some duct tape on the end of a piece of wood (like a paint stir stick). That at least would let you get and hold your magnet in place until the glue sets.
