If you look at Seeley's work on swarming you will see how that works. All though he is working with small colonies it still applies to larger colonies if varroa has not had free rein up to the summer artificial swarm. Splitting a colony early spring with all open brood and the queen in one half on the original stand. The other half, being mostly capped brood and producing it's own queen, will reduce the mite numbers enough. Recombine those after the new queen is laying if you choose. Timing is important and you would have to see if it would give you the desired results in your location. Being this is a TF, treatment discussion, you could use a flash formic or oxalic dribble during the open brood or/broodless period.I would lean towards the latter, because according to SiWolKe he is claiming that creating an artificial swarm mid summer is as good as any treatment.