Praise be to Allah
I put this question to our shaykh, ‘Abd ar-Rahmaan al-Barraak (may Allah preserve him) and he replied:
It is not permissible for him to give some of the meat of his udhiyah to feed the poor, with the intention of expiation for breaking a vow, because he is giving that meat for the sake of Allah, so he does not have the right to connect another matter to it that is obligatory upon him. Rather he should eat from it (the meat of his sacrifice), give some in charity, and give some as gifts. End quote.
Ibn Abi Shaybah narrated in his Musannaf (12563) from al-Hasan that he disapproved of a man giving some of the meat of his udhiyah to the poor as expiation for breaking a vow (kafaarat yamen). End quote.
And Allah knows best.