I would usually have people get really used to heel sliding down the hill with one foot out, just to get used to the pressuring needed to slide vs. stop. Once they got good at this, I would literally have them do some squats while moving, to get used to moving their upper body up and down while keeping the pressure the same on the heel edge.
I call it the "squat and skid"
My dog uses a similar technique to leave his weaponized ass juice on the carpet.
That way, with the unfit ones, you can have them grab the toe edge or boot or something with one hand just to get some weight forward/leverage, then in one motion, push off snow with one hand and pull forward with the other. The key point was using one motion to "throw" themselves into a heel skid and actually stand up while the board is moving a bit. Not locking the knees is huge as well, cause that will just put them back on the ground.