I sometime use a "frame filler" inspired from this site: (sorry french speaking)
http://www.frenchbeefarm.com/framefiller.htm
and a video
http://www.frenchbeefarm.com/video_remplisseurdecadre.html
I build my own frame filler with a plastic laundry room sink, two drilled PVC pipes an a gas motorized water pump who recirculate the syrup from the sink to the pipes. That's was working great but you need to add a good filter on the system, because the debris (bee legs, wax...) will soon block the hole in the pipe. I use an old water filtration system filled with cloths.
If you recirculate the syrup for a moment, it get hot and that create a real frenzy when you introduce filled frame in the hive. And that's true, filled frame are very heavy.
I stop using it for a few reasons:
-I used it in early spring (mid march), and here in Quebec, humidity is the main concern in spring, wasn't a good idea to introduce so much humidity in the hives.
-I feed generously at falls, so the girls doesn't need so much food in early spring.
-in that time of the year, everything is covered by snow. It's difficult to drive a truck to the field with barrels of syrup, sink gas pump etc...
-it' 1 million time more easy to carry a few pack of candy, introduce them upon ventilation hole and bring back the insulation sheet on the hive without disturbing the bees, if they need it, they will go get it.
-by filling a lot of frame from hive to hive, you get a lot of chance to spray AFB if present. A big part of the syrup sprayed on the frame is recirculating in the system.
your idea of giving them to nucs is good, but be careful if you move the hive, if shaked the syrup will flow out from the cell. I try one time to fill the frame at home and carry them to the field an I did a real mess.
this is all my experiences with frame filler, hope this will help.
Pascal Fournier