My horses just kind of pick up liberty work. Whenever you're around them, just ask for things without using the rope first. Pretend that there isn't a rope there for your initial request, and then back up your request with the rope. Soon, the horse will respond before you have a need to use the rope at all. The test comes when you take the rope away and you don't have that safety net anymore.
I don't usually set out to practice working without a line. If I do anything like that, it's on a sheer whim, like I'll be practicing showmanship and just take the lead off and see if my horse can still do the pattern without me touching him. Or, when I dismount after a ride I'll leave the reins looped over his neck and let him follow me. It doesn't look like much, we don't do anything too dramatic, at least not yet with Scout. My first horse could do NH lunging in a fairly open area without a line, but that was after a few years of just doing "normal" things with leads and lines.
IMHO, things like liberty and tackless work are just a function of good training, no matter what the label. I know some old trailbusters who have never heard of Pat Parelli or join up who's horses could be ridden bridleless and would work without a lead rope.
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown