Insulate and feed.
A poly nuc would be an improvement, but a wooden one, not much of an improvement if any.
You'd likely be needing an extra nuc eke for feeding - if you get a Payns polynuc, I'd strongly advise blocking off and not using the integral feeder at all -- you can't clean it out without removing the bees to another hive!
As part of the 'insulation' concept, you could reduce the hive volume with a block of insulation board. A super filled with insulation over your feeder should help.
Feeding. 2 pounds of sugar to 1 pint of water is about as strong as you can go. Metric 2:1 doesn't fully dissolve.
Strong syrup is for storing, rather than immediate consumption.
You need more comb drawn to store it in. So a weaker syrup (like metric 1:1) could be a better bet for now.
Consider using an emulsified Thymol tonic in the syrup. (Search the forum for lecithin, and look in the Stickies section). If there is a Nosema problem, it could help. If not, at least it'll prevent the syrup going off!
For later feeding (for fast storing) Ambrosia (and similar special bee-syrups) are excellent. Though more expensive than sugar, they can take it faster and later than sugar - which makes it worthwhile in my eyes. Plus it doesn't go off or ferment - you can store any surplus for next year - there need be no wastage!
Contact feeders have disadvantages - but one advantage is that the bees will take syrup later from a contact-type feeder than any other type.
It would make sense to organise where you can get some (plain white) bakers fondant from, for use later in the winter. Most cake shops are happy to get in a 12.5kg box for a beekeeper, and expect to be charged up to about £15.
