Is it permissible for someone praying at home to offer a supererogatory prayer (nafilah) at the time of the Iqamah for an obligatory prayer?

Al-Bukhari and Muslim reported on the authority of Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: "When the prayer is commenced, there is no prayer except the obligatory one." Accordingly, it is not permissible to begin a supererogatory prayer after the iqamah for prayer has been called, except for one who has a valid excuse for not attending the congregational prayer.