A jig you can use to attach a magnet directly in the center of a 32mm model base. 

Glue a 6mm x 1mm magnet into the center insert, making sure to match the polarity of any existing magnetic bases in your army. This magnet is not completely flush; it protrudes slightly to ensure that a 2mm thick magnet placed on it makes solid contact with the underside of the base when pressed down onto it.