go for it!
Like Showjumper I'm training my mare to ride in a bitless rope halter with reins attached. When we initially tried it, she had no idea what I was trying to achieve and it was a huge battle.
However, I went back to basics....try teaching your horse basic flexion exercises with your normal halter & leadrope. Do this first from the ground by standing at the shoulder and asking for her to move her head in your direction.
Initially it may be more tugging than asking, but pretty quickly the horse will get the hang of it. When you're satisfied with her response, hop on and do it from "on-high".
IN order to teach stop you need to be on board. Lets say you're walking around the arena and you're following the movement of the horses walk. Stop following the movement and release the energy from your body, then at the same time pull the leadrope rope towards your body. This will actually cause the horse to circle slightly in the direction of the pull and they will have to stop.
My horse (who can be quite stubborn) now knows that when I stop following her movement, she's meant to stop and it requires very little for me to stop her at that point.
I've taught her this in the last month or so, but I havent taken her hacking in the halter....I'm a bit nervous about it...old habits die hard I guess. However, in a couple of weeks I'm taking her on Exmoor and I'm gonna do it then!! Honest!!
If its any help to you, my mare is rising 5, very dominant and sometimes prone to the odd spook. I like the idea of bitless because I want to save her mouth and she really didnt like having a bit in there.
good luck with it!