Don't think the augmenting captain need to be RHS-qualified, at least the way EK is doing it now. The FOs aren't LHS-qualified and that's why the pilot that is PF at any given time should be in the seat that he/she is qualified for. That raises the question though, what if the PF needs to take a "comfort break" during the time let's say a FO is in the LHS? That leaves only the PM now also PF in a seat that he/she is not qualified for.
Correct.
EK OM-D 2.1.3.6