The General Instruction on the Roman Missal (GIRM) for 2003 says:
The diocesan bishop or anyone equivalent to him in law must be mentioned by means of this formula: una cum famulo tuo Papa Nostro N. et Episcopo (or Vicario, Prelato, Praefeto, Abbate) (together with our servant N., our Pope, and N. our Bishop [or Vicar, Prelate,Prefect, Abbot)."
However the diocesan administrator is not the equivalent to a diocesan bishop as seen in canon 368 which refers to holders of stable offices even though the diocesan administrator has nearly all the faculties of the diocesan bishop according to canon 427.1. Thus I think it is incorrect to include the DA in the canon as he is not the holder of a stable office. I`m sure a DA needs prayers too but I think it confuses things to mention him there and the omission in the canon of the ordinary`s name brings home the notion that we are sede vacante.