Hey,
Go ahead and pick five schools on test day. Your chosen schools won't automatically get notified of your score--what you're actually doing is giving those schools permission to view your score report if and when necessary. In most cases, schools will trust the score you report on your application and only double check the score with GMAC once they've already decided to accept you. Otherwise, schools would need to take the time to check each and every applicant's score. Also, when schools view your score report, they get to see all of your past scores anyway. It just makes sense to save yourself the fee and pick five schools on test day. Hope that helps.
Best,
Matt Mapplebeck
Student Services Associate
Manhattan GMAT