Yoga offers students an opportunity for balance. That balance transcends the concept of standing on one foot. It is the bigger picture balance.
Since we live in a society where the hip flexors are commonly shorte(ned) and not contracted, since we live in ways that increase chronic low back rates due to spam or lack of integrity in the aforementioned muscles, we must use care in working those muscles and perhaps not do so routinely.
If they must be worked (periodically) then the student can begin with Dandasana, Purvottanasana, Urdhva Prassarita Padasana, Ardha Pavanamuktasana, then Ardha Navasana. In addition, if you are well trained, crafty, and have a wall rope system you can set students up in Navasana at the wall with the soles on the wall and the arms holding wall ropes. This could be done with two belts, a foam block and a door, as well.