Is it permissible to perform qunut in supererogatory prayers, such as the regular Sunnah prayers and the absolute supererogatory prayer?

Qunut is authentically reported from the Prophet, peace and blessings be upon him, for calamities (nawāzil) in all prescribed prayers, and in the last rak'ah of Witr. As for qunut in supererogatory prayers (nawāfil), it has not been reported from the Prophet, peace and blessings be upon him, nor from his companions. Imam Al-Shafi'i explicitly stated its impermissibility in supererogatory prayers, except in the case of a calamity, in which instance it is not disliked. However, it is not legislated. Thus, qunut is not legislated except in Witr. The qunut for calamities is legislated in obligatory prayers, but qunut is not legislated in regular supererogatory prayers (rawātib) or unrestricted supererogatory prayers.