thank you for your thoughts, it was a quick and rough idea. I don't have the technical background and surely can't figure out the details.
i don't think there is some kind of force needed. the relay returns every now and then an ad into the stream and the user has the incentive to "earn" some sats for watching and maybe even support the relay operator by splitting.
of course there will be clients that are AD free, no matter what an relay is returning. or you have a client side setting the user can use to hide ADs (see screenshot).
thanks again for the discussion