If you really don't want folks to use the SoG's as dead cards, simply make it impossible to happen.
How about forcing folks to use
Mark? That should anyway be the spirit of this turney, as that would take the full potential of the SoG's.
Another option would be that the decks would have to be "War Legal for team Life".
As I understood the current rules, I thought it was encouraged to take some SoG as dead cards in order to get multiple copies of any card you want, if you chose not to go for a SoG deck.