"he makes special plays perhaps only 5% of the time, how many thousands of hands of video poker would he have to see before each "special play" was made?"

5% is once in every 20 hands. If he played 4000 hands in a session that would be 200 special plays in one session. That's 200 hands that reduce the expected return and does not include his errors that are on top of the special plays. These plays will shorten most sessions and lead to less session wins (the exact opposite of what Singer claims (ie. his claims are a lie)).