How big are the qtrees you are planing to move. I can think of ndmpcopy but "how long" is something difficult to predict. NDU is not possible for CIFS wether it is qtree/volume due to it's nature (unless it is continues share). I am not sure if this idea will work - flexclone->delete rest except the qtree you need --> split it...dosen't sound good, splitting for a large volume is very slow, so I wouldn't go that route.
I guess, use ndmpcopy or another tool (host side) to copy the data across. With ndmpcopy, you can do base line and an increment, shutdown cifs, do another incremental. Re-create shares and restat cifs. Let's see what others suggests, I am sure there will be other ways that I am not aware of.
