The wise V12 owner, once he gets that old plug out, will take a brand new plug and cut the lugs off of it before installing! Then fashion a tang secured under a nearby bolt head to hold it in place, applying some light pressure to ensure a seal.
Thing is, though, I had concluded from your photos that this had already been done!
BTW, there’s an even better fix now. John_John1, who resides in Lithuania, has been fabbing plugs out of aluminum: