I say, and with Allah's success: There is no making up for the Sunnah prayers except for the Sunnah of Fajr if it is missed along with the obligatory Fajr prayer, in which case it is made up for commendably. The Sunnah is not made up because making up is for what is obligatory in the account, and the Sunnah is not obligatory to the extent that it needs to be made up. However, if one prays for the sake of Allah, compensating for what they missed from the Sunnah, it is permissible. And Allah knows best.