In order to give instrument training which is logged as instrument dual received and counts toward the required dual training, you must have a CFII. There is only one exception: A CFI may provide the instrument instruction required for a PPL.
However...there is nothing that says you cannot GIVE all the instruction you want or act as safety pilot. It simply cannot be LOGGED as dual instrument received. Since you need more "instrument time" than dual instrument time for the rating it probably would not hurt to start early (logged as SP). Legally he could go up a private pilot SP and shoot practice approaches today...so why not go with you?
Many programs start with sim...you may not want to do that, since it cannot be logged at all without a CFI. While the training might still be useful, the student may not want to spend the $$$ and not log it also.
Also you mentioned 141...you would need to talk to your CP, but I'm fairly certain that 141 will require a CFII to do any training that counts towards a 141 program... they usually start with SIM anyway. If you want to start early it probably needs to be part 91.