You an simply use a ferrous metal housing, such as a proper size food can and attach mount it over the rear magnet. However, if their is a vent on this driver you will need to drill a hold in the back of the can and insert a tube to route the vent to beyond the can shell. Before permanently installing the can, put it on temporarily and hold the speaker near the tv and make sure it has no effect whatsoever on the monitor.
You can also use a bucking magnet, but I'm not sure who sells those at the sizes you would need for this application. I''ve never had a need to retrofit a driver to make it magnetically shielded.