Ari Seppala suggests' keep a colony thru the winter headed by an unmated queen, adding frames of normal brood to keep the population up'. Others have suggested importing drones from stocks adapted to long warm seasons, whose genes would surely be ill-suited to short northern seasons.  
Surely the drones produced by an unmated, drone-laying queen will be of poor size, reared in worker cells by a demoralized colony.   Would not the 'natural' way be to overwinter a selected colony in a (gently) warmed bee-shed with a tunnel entrance to outside, and feed dilute honey (not sugar) plus pollen patties in spring to force on 'natural colony development', then insert frames of drone foundation at the edges of the nest? 
This is only a suggestion - we have not had to develop this technique in the more southerly UK climate. 
Robin Dartington. 

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
-- Visit www.honeybeeworld.com/BEE-L for rules, FAQ and  other info ---
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::