Hi greenfig,
I'm no expert in cloners. But I've been rooting for some time now.
It depends on what we consider a rooted cutting.
If you're speaking of a cutting with 4 1' long roots... Just forget about it. Last October, I had a damn Panaché cutting, still green but not doing much. I thought , before winter can kill it, lets check what it has done.
It happened that the cutting had one root. Of course while putting the dirt back, the root just snapped ... Damn fragile and precious those things when there are few ...
If you're speaking of a cutting with a root-mass like a (small) ball of wool. Then bag the root-mass in a zip lock and put 2 wet paper-towels in the bag.
You should be good for a 3 days trip - well that would be ( now ) when the temps are neither freezing nor cooking-like.
I wouldn't add soil, as soil will help break the roots when shook on the postal-trip.
If I would use some soil, I'd use perlite as it is light weight .
That wouldn't be the safest trip, but I think that it could be reasonably achieved. - After all, nurseries send bare-rooted trees (at the right time and that is now or sometime in the following weeks), and your cutting would (have to) look and act like a bare-rooted tree.