The one year I had a KTBH, they did not flourish and went into the winter with inadequate stores. Just before the weather got cold, I spread out a few bars, putting spacers at the ends so that the gaps led only upwards. I made a slim rectangular wooden frame (maybe 2 cm deep) that lay horizontally above and on the bars, such that the upward gaps were within the frame, and covered the frame with a piece of glass. I had put insulation in the cover, and removed enough to provide space for the frame under the cover, and got some cloth or burlap to loosely fill the extra space around and above the frame for insulation. I put slim slabs of fondant in the feeder, which was warmed and accessed by the bees up through the gaps. The cluster stayed under the gaps, and they were in the feeder chamber all winter. The glass allowed me to inspect the chamber, which didn't hold more than a few weeks of fondant. It was a very mild winter, and they survived nicely, probably mostly on the fondant. It was an act of desperation. If I tried another KTBH, before installing bees I'd cut gaps in some of the bars, and work out some sort of permanent cover/quilt/feeder above the bars. I've seen several variations on this idea on various internet forums, all better than I expect I could do. Look for TBH quilts, and consider adapting them as feeders.
This hive showed little interest in side syrup feeders and no interest in side or bottom fondant or pollen patties on a follower board. I gave up on it because I could not solve ventilation deficiencies, possibly caused by my climate and siting. I believe it also had a mite problem I wasn't able to deal with effectively.