My personal preference since they are dormant is to plant in the soil and baby them for the next few years. The root will probably not be blooming size until the time you are intending on moving.

One of the things that some discount when mentioning moving pots into unheated areas during the winter is that without some moisture in the pot the planting medium acts to pull moisture from whatever is in the pot. If the roots are large little change may be noticed but for younger things it could be damaging. If the medium is pulling away from the sides of the pot you need to add moisture. There are two reasons for this in my mind. The plant may be damaged as I just stated. When it comes time to put the pot outside depending on the medium the outside material can become very wet but the inside with the root remains dry. I lost several citrus trees this way thinking that they were waterlogged. You can try the old thing of putting a small amount of liquid dish soap in the water which can break the surface tension that keeps the medium from absorbing moisture. The other alternative is keeping the planting medium slightly moist over the winter so that any moisture when placed out will spread throughout the whole pot.

I agree with maifleur, plant them in the ground. Yes, they'll be set back a bit when you move them in 2 years but they're a heck of a lot easier to keep alive in the ground and will make better progress for that period than they would in pots. I have several in the garage now in grow bags (late sale at Adelman's last fall, ground was frozen by the time I got them), seem to be easier to judge moisture rather than pots but still a pain!

Thanks!