OK so I figured it out. So how do I make it return the opposite?
This returns anything that has a internalRating:
$searchWADAtimes_1->setSearch(array("type"=>"Value", "comparison"=>"<>", "join"=>"AND"), array("times.internalRating"), "s", "" .(isset($_GET["excludeRS5"])?"WA_BLANK":"") ."");
I've created a checkbox that says Without Rating, which is "excludeRS7"