> Given that simple truth, the only "expressive" claim that the copyright holder could make would be that "there should be an ad of some sort here."

Or he steers away from that and states "my program places an Ad here, removing this operation modifies my work", making not the Ad itself part of the work but the process (and outcome?) of an Ad being placed there...

I do hope there's a better legal conclusion the court can take here. If I am legally required to execute arbitrary code on my machine as part of some openly accessible content, I expect a clear contract to be agreed upon...