"Choruses tend to get stuck in your head because they are the bit we know best and because we don't know the second or third verse, the song remains unfinished. Unfinished thoughts are more likely to return."

There's a whole new approach to try. Perhaps the earworm is the work of your Inner Nag, who is scolding you for not learning the whole song. Try learning the whole song and singing it through. Perhaps your Inner Nag will shut up about it.