Seems like this could be handled with a fairly simple rule that a NT manager can't call more than one of his own players.
During previous WC NT manager of China called at least 3 (maybe 4, or more, I didn't focus on that) own players, the same as NT manager of Ceska 2 seasons earlier. I think it would be hard to prove that they were saboteurs.
Afaik at least last five in row (and probably more) NT managers, who won last five NT WC, called at least one own player. It means that NT managers, who don't call own players, should be banned ;-)