all light had to do is instead of tell mikami : "dont do any unnecessary until today" he should have told him "do not dare to use the note book until today no matter what happenes got it?" also light could just told mikami to save a piece of the note book b4 he was taled by gevani (only light and the other death note users had the knowledge that a piece of the notebook have full effect) , this will work only if NEAR woudlnt use the real notebook on mikami b4 they came to the meeting place.