Re: Filling comb with sugar syrup.
Filling comb is an old idea, and it works pretty well as emergency feed.
It's time consuming, messy, and doesn't work all that much better than a candy board, but it is easier for the bees to get to the syrup. Probably only possible to fill one side properly, it will spill out if you flip the comb over.
There is no need to worry about inverting the syrup, the bees can use sucrose just fine. They make honey by inverting the sucrose because it stays liquid better for winter storage, but filling comb with syrup is emergency feed, not overwinter prep!