I put a super (10 frames config) of Permacomb on 4 hives. I sprayed each frame with a 1:1 mix of sugar-syrup and HBH. After about three weeks all the bees have done with it is build comb from the bottom of some of the PC frames to the top of wood frames below. How do I get the bees to accept it and use it for honey or brood?
(BTW: I used 12-lb fishing line pulled between the boxes to separate the PC super from the box below. Fast, works great and practically no mess. The bees didn't seem to care: my theory is that since the bees have no pre-programmed/instinctive response to such an event they simply don't react).
Sounds like they don't need the space yet. When they do they will use it up fast. The first step is for them to connect the two boxes with bridge comb, once they do that they are on the march upward. They will be busy cleaning and polishing it for a while before they start storing in it.
I have more of a problem with them making a chimney up the center, but they are all a little different.
Your fishing line idea is a good one, I'll have to try it.