"what about keeping small tubers in a pot with soil over the winter, in the same way? "
I experimented some years ago with using potting soil as a storage medium for tubers. The tubers were fine but they all grew huge piles of hair roots and that would mean to me that the hair roots would have to be removed before shipping and that is a another step. I also would worry that they would not sprout very well after the loss of the roots.
Having said that about storing tubers, what about your proposal to "pot up" the tubers but not water them and store them in the pots until spring? I bet that this would work rather well but you need lots of potting soil and time and then space to store the pots. Try doing it and let us know. I cannot imagine it not working but all things new have unknown pitfalls. 
