As of now the only way to disable prerolls is to run three minutes of adds per hour. So viewers wont stay if a preroll comes up and leave if a 60 second add comes up every 20 minutes ( I know I do ). So maybe a 'later preroll' option that requires maybe 90 seconds of adds per hour will a 60 second preroll that will delay starting untill about 3-5 minutes of a viewer watching? So a viewer begins watching for 3-5 minutes to see if they will even stay, then a 60 second ad, then a 30 second ad every twenty minutes.