Last fall I pulled up, tapped off, and heavily pruned most of the geraniums, then tossed them in a box and stuck them in the basement all winter. They got maybe a couple drizzles of water, but remained dormant until increasing daylight hours was barely noticeable through the small basement windows - and then they started to wake up. The plants look pathetic, but were still leafing out and even blooming.
Last weekend I cut a bunch of the new growth, removed any flowers, and stuck the cut ends into pots, forgetting to even dip them in rooting hormone.
So far they all look fine under their plastic covers and grow lights, with a heating mat underneath. I don't know if they'll successfully root, but it doesn't look like any are dead!