My bees are currently drawing frames and filling them in the super. What I want to know is how to feed this back to them.
Don't understand the reasoning behind this.
Why? Sounds very much like making them extra unnecessary work! Let them continue to collect. More honey stores equals less you need to feed later. Consider what would the bees be doing if they were not being poked and prodded by a beekeeper.
You could simply leave it on over winter as a brood and a half. Remove the QE as, otherwise, they will leave the queen behind if they have to move up into those stores.
Where would you expect them to put it if you feed it back? Sounds like they may need to draw another super to put it in! If they fill it, put another one on. We are only in the middle of August. If you have the flexibility of spare stores, you are in a good position to prepare for winter without worrying so much about timing of winter feed, if even required.
In your shoes, I would not put another super on. I would remove any capped frames (at the few inspections) and replace with another frame (drawn comb, if possible).
When the time comes for making a feeding decision, you might have several honey frames you could simply replace. You might think, 'I'll have that' and feed back sugar.
You might want to remove any capped combs at that point and feed sugar to fill the super. You may wish simply to remove the super (if about full), feed to fill the storage in the brood and then replace the super, knowing it to be proper honey which can be part of next year's crop.
You could mark any capped frames of honey (simple drawing pin into the top frame bar?) so that you can recognise them easily in the spring.
A super on the brood will leave more than enough stores for the winter. You could winter on the brood only. I prefer not to - the reason being that outside combs, of stores not used, afford a degree of insulation if the cluster is central. You would less likely to be needing to feed in the spring for brood expansion (simply scrape open some capped honey).
Possible your bees will only consume 10kg of stores over the actual dormant months, but you can never bank on that scenario unless you are prepared to feed early in the new year if things don't turn out, for instance, as benign as last winter (the really quiet period was only about 6-7 weeks).
Lots of alternatives. With one colony yours are limited somewhat, but that is life. half a dozen hives is a much different story, but still the same applies.
'Molly coddlle' your one colony. Keep it warm, sufficiently ventilated (to prevent any damp), enough food for the duration, without any spare 'head-space' (warmth rises and the heat leaks out), healthy and it will almost certainly survive the winter strong and expand ready for the early spring flows.
Regards, RAB