How about something like this?
I use something similar for mountain biking. When filled, it is relatively flat, so could be placed under the top, above the bars. The tube could be inserted into one of the top bars, or the side of the hive for feeding. A feeder/feeding holes would have to be designed for the end of it. The bag can rest on top of the bars and filled without disturbing the bees. With the top screwed on, a vacuum is created so flooding of the hive is less likely. Still could be a problem with cold weather.
Or Google for "100oz Omega" if the link is edited out. Pricey for a feeder, but no waste (no empty baggies). I'm sure there are cheaper one available.