The typical shipping method works fine: packing moist paper around the base, taping up to keep the moisture in, etc.
I would imagine that, as long as you wrapped the roots in moist paper, then wrapping them in plastic, bareroot would be just fine.
Barb

Somewhere, can't remember exactly where, the following idea for small seedlings:
stuff a bit of crumpled (moistened) newspaper in bottom of cardboard toilet-paper roll, add a little soil, insert roots of seedling, sift in a little more soil, tap lightly to settle soil, wrap in wet newspaper, then in plastic supermarket bag, with twist tie at "neck" of plant, then into box with some plastic bubblewrap or biodegradable peanuts.