This would be another option to get some "young" bees in your nuc. They will be more likely to stay put then those that have already been out of the hive.
Take a few frames with eggs and larvae from your existing colony and shake off all of the bees. Replace them temporarily with empty frames. Put down a queen excluder, then another empty box. Put the frames with eggs and larvae in the empty box above the excluder.
Come back the next day and you will have young bees on the frames above the excluder tending the brood. Shake all of these bees into your nuc. They are more likely to stay in the nuc since most of them have never ventured out of the old hive yet. Then you can put everything back the way it was.
If you can spare it though, even one frame with open brood will have a tremendous effect in your new nuc in keeping them content and fixed to their new home.
To everything there is a season....