I’ve also just winging it. My riding mare does not like longeing, so it’s hard to get her to lock onto me in a larger arena for w t c. The nonriding horse I currently care take turned out to be a genius at free longe and will w t c a 20 meter circle at liberty on voice or hand cues. Also whoa. My riding horse learned all kinds of clicker tricks and can do performances for children and will go over obstacles on hand cues at liberty like go stand on a mat, go stand on a box. The nonriding horse loves doing lateral work at liberty for treats, but she gets bored doing tricks. The riding horse will hyper focus on a trick training session and so you can shape her behavior (we went from her natural behavior of pulling halters off the stall door at feeding time to playing fetch with a glove or hand towel). Nonriding horse gets bored after a few tries and starts to switch things up. She enjoys them, she just doesn’t like repetition and thinks she should offer something new.
So my experience has been that you need to go with the flow of what the horse likes to do, and figure out how they think and feel.Cavallia the traveling Cirque de Soleil spin off, has 60 horses because they are all really “one trick ponies” that do one act really well
Because of this, it’s such a great way to get to know your horse and how they learn and think. And build on what they naturally do.
Walk trot back half walk on turn “leading” with no lead rope is a great start, as long as there is no distraction like grass in the arena 
it’s a nice thing for both of you that shows how much your horse is already tuned into you.
Like any training, you do need to “get into the zone” first and gauge your horses attention and focus. For instance do all the leading pattern with a slack lead rope, letting him mirror your movements. Then toss the rope over his neck and repeat. Finally if you’re alone in a safe enclosure take off his halter and repeat. But if he’s distracted by wind or barn chaos that day, he might never settle and that’s OK too. You can’t force liberty work if his head isn’t in the game that day.
I’d say everything in liberty or clicker requires that you teach the thing and its release or opposite. So you want a cue or context to follow you, but also one to send him away from you. You can base that on whatever you already do to longe. It sounds like he is on some kind of rehab rest so you aren’t going to want to do trot and canter, but you can send him away from you at the walk first on the longe line or a very long lead rope then with no rope. You want a signal to come back to you (I like to whistle) and a verbal whoa. The point of this is otherwise you get a horse that’s just glued to you which is limiting.
Another good one is whoa and stand. You can build up to this with a lead rope, then toss the lead rope over his neck and walk all around him, walk away, walk back. Then add in whoa and then have him wait until you whistle to come to you. I find this works best when you can Intuit how long he is going to stand before he gets impatient and moves, and reward or release him just before he gets to that point.
After a while when you have the basics transitioned to liberty you can add on new tricks at liberty but in the start you are transitioning from things you already know with a halter to doing them at liberty.
I enjoy it because there’s no real end goal, just finding out what works with each horse.
