It is not permissible; because the essential element in the Zakat al-Fitr is the ownership transfer to the poor; as stated by the Prophet Muhammad (peace be upon him): "Give on behalf of every free person and slave," in Sunan al-Daraqutni 2: 150. The act of giving is the transfer of ownership, and it cannot be fulfilled with permissible food or with something that does not constitute ownership at all. See: Bada'i al-Sanai' 2: 74-75.