It might be worth going back to the original post here before everyone gets themselves tied in knots:
But what if you are flying solo and elect to fly IFR: can you then carry out an IAP in VMC, or do you have to go for a visual approach?
He's IFR - it has nothing to do with flight conditions - he's IFR, end of story. Quite entitled therefore to fly that IAP no matter what the number of people on the flight deck.
Now follow this reasoning. If someone is ostensibly VFR but asks for an approach for training then effectively they are putting themselves IFR.
Reason?
Either you're going to vector them or they're going to follow a laid down procedure. Either way they stand the risk of going inadvertant IMC due to the nature of the task. On that basis they effectively become IFR, and therefore get treated and handled as such. The term VFR implies the guy can deviate from track and level at will to remain VMC - this has no place in the scenario so far, so isn't applicable. Telling that person to remain VFR defeats the object of the exercise.
As for the missed approach scenario - there would be nothing wrong with the phrase "In the event of a missed approach turn left/right into the visual circuit VFR". That removes the ambiguity as to what rules you're on during the approach, but provides a non-separation required solution at the end of it.