Out of curiosity… this question was downrated why?

His counselor can sign it. Part of the process is answering the questions and signing your name - in the mouth of two or three witnesses, etc. Everyone has to sign his or her own name to the slip. If he signs himself on another line, that's taking away one of the witnesses.

A bishop would normally be interviewed by his Stake President and the SP by the Regional President / Authority.

This is very interesting. The Church Handbook of Instructions doesn't say anything about this however the 'temple recommend binder' might do. It would seem that the counselors could do this accordinf to the below quotation a Bishop or Stake President comes under a 'ward member' so could be interviewed by counselors. However the Stake President would probably be interviewed by his Bishop and not a counselor and the Bishop would probably be interviewed by the Stake Presidnet. "In Wards and Stakes The bishop, or his counselors as authorized by him, interviews and issues temple recommends to worthy ward members. The bishop personally interviews members who(1) are preparing to receive their own endowment, (2) are planning to be married in a temple, and (3) have not lived in the ward continuously for at least one year. Only in the most urgent cases when he is absent may he authorize one of his counselors to issue recommends in these circumstances. Following the interview by a member of the bishopric, a member of the stake presidency interviews the person and signs the recommend if the person is worthy. The stake president personally interviews members who are receiving their own endowment and members who are planning to be married in a temple."