The first idea doesn't work; tried it.
The second idea, unfortunately, also wouldn't work. First, you'd have to make the minimum movement speed 0, which it isn't, but even when you made it that, whenever a unit hits exactly 0 movement speed, it can no longer turn.
I had a working solution for a while that involved making the unit able to move, and creating a pathing blocker at the location of the unit so that it could only turn while attempting to move around, but I don't recommend that system at all.
If nothing else, if you don't want a Sell button (to use Root for), you can change the Root abilily to be a black icon with blank tooltips, and make a small trigger to cancel unroot whenever it's ordered to.