Is it permissible for the Imam to sit on a chair and deliver the Eid al-Adha sermon while standing, without sitting between the two parts of the sermon?

Perhaps the Imam is following the opinion of those who believe that the Eid prayer has one sermon, contrary to the majority of scholars who say it has two sermons. Sitting between the two Eid sermons is a Sunnah according to most scholars, and the two sermons themselves are a Sunnah, meaning the prayer is valid without them. Therefore, what the Imam did does not affect the validity of his prayer nor the prayer of the congregants.