Sorry Tibor - thanks for your bump
I have no Meshmixer solution but modeling hair by hand.
If your scanning result offers an overall texture the new features of Texture to Per-Vertex-Color transfer in MakeSolid and expanding a selection to similar color in SELECT to face-group hair strands might help, but basically all has to be done manually.
Know you use SL scanning. Photogrammetry or Primesense (e.g.Kinect) based reconstruction technics are more robust, but not optimal scanning hair.
EDIT: Forgot to mention:
Using SL you might try a low resolution cam. Results will be not detailed but you'll get the overall shape better.