Franco also modified the game's script, so once you enter a Leviathan helicopter it automatically adds the magnet (just like in the original mission). It was mentioned and linked somewhere in the Braindead topic, but I can't be bothered to dig out myself. Just thought I'd re-direct you if you're having problems with the other ways. It doesn't count as modding as long as you stick to Leviathan only, all other helicopters can not have that magnet (they can with a mod, so rather avoid that).