So if I am understanding your post and assuming you are in a figure 8 going to the left, you would press with the right leg in the center of the flank as you approach the "X" to create bend, then use the left leg back to push the hind end over as you ask for the right lead. Once you switch to the left leg, you quit pressing with the right leg. Is that correct?
First I never work leads in anything but a straight line.
Lest say a horse is on the left lead. I want their hip to the left. So the horse has a nice arc going to the left. Now I will practice this and not change leads. This keep the horse from anticipating. Then when I do want the horse to change leads I remove my right foot/leg and apply my left to shift the horses hip over and then I open up my right leg to give his shoulder a place to go. Once the horse gets it there is very little you can see. Most of the time a finished horse does not even need the left leg as they will already have a nice bend to them with out it so all you need to do is apply the inside leg to move the hip over and pop the outside leg so they know when do to actually change.
I do basically the same thing. If I am on the left lead, I want the horse bent to the left. When I want the change, I slip my inside leg back to push the hip out, sift my weight to the right, and move my reins across the neck for the direction change. That sets up their front and their rear for the change. Some of my horses only need the leg cue but I like to combine the two cues because sometimes I like to move their rear at the lope for positioning purposes on the trail and I don't feel like a flying change when I'm trying to move their butt.
I wrote a few different variations. Explaining it is harder then I thought LOL
This is the best way I could explain my method.
If I am loping to the left, I'll turn down the middle of the arena, straighten the horse. I'll keep my right spur pushing into them at this point(not hard, but there is pressure), as I near the center, I wait until I feel their left hind extended (as they are now in position to easily switch), and then I'll switch my pressure from my right, to my left(as well as my body, slightly, helping them to open up). Once they switch, I keep them going straight a few strides, and then turn them to the right to continue on.