When I ground drive, I use the rings just below the top ring. I then pass the offside rein over the horse's back and drive that way. It puts the reins more at hand level. It also is easier to do trot and canter work as the offside rein isn't hitting the horse on the hock. As the horse gets better, you can easily do trot (and later canter) figure eights. I do lead changes through walk before I ever get on a horse's back.
You stand in the middle of the ring and drive from the side (like longing). To turn, you steer him a little towards the center of the circle and then turn him to the outside in a half turn. Lift your hands up and allow the reins to pass over the back. At trot and canter, you will have to run a little until the turn is finished, but that's all. You can drive all gaits that way without running behind the horse.
I am getting ready to start a young gelding soon. Maybe I can get someone to video this method, if anyone is interested. It will be in warmer weather, I ASSURE you!!