Monitors

When there is a TV broadcast - like news etc. etc., there usually are monitors so that the person who is on the show can actually see what the camera is showing. Garth could have looked at a monitor and read the cards.

what about Noah's monitor

Then why didn't Noah see it on the monitors.There are usually more than one so that everyone involved can see whats going on. Im sure he would have glanced over at one of them during the interview and caught on, otherwise Noah is three deaths short of a scream movie (stupid) in otherwords.

noah is a gimp

Noah Vanderhoff is a gimp, remember? He is basically an out of touch guy who got lucky in a new technology, remember he used to be in meat packing? Alongside that he would not have much experience with television apart from his tv commercials (which are, as we have seen, pathetic)AND even if he knew where the monitors were, he was too busy answering Wayne's questions to glance off screen, fter all he has a public image to uphold. SO, its very plausible that the monitors were within eyeshot but Noah didn't look there (especially when you consider that they weren't even allowed to nod their heads when the countdown to airing was being done...imagine having someone glance off screen!).

There may be a more obvious solution.

Perhaps Wayne told Garth about the writing of insults on the back of the cards before they went on the air?