To be able to mill while standing upright would be great, but it's not going to happen in the woods.
For me to stand up straight, the log you were milling would have to be a foot higher.
Log doesn't have to be much or at all higher - the handle positions and heights on the mill are probably more significant, as shown on this picture.
It's mainly the left hand being up by 8 -10" and closer into the log by the same amount that makes the big difference. The right hand doesn't need to be much further up but if it can be lifted up it can also be moved out to the right a bit to improve leverage. An MC or aux throttle is not really needed, a cable tie over the trigger would for most purposes work as well - I have done this with my mates 3120.