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.