If one examines the entrance to the feeder, it has a really narrow slot through it, longer than the entrance is wide.
A thin piece of scrap plastic (as from an ice cream tub) can be cut to size, stuffed into the slot, and the entrance to the feeder neatly closed off.
And the 'modification' can be undone in a moment.
Now - what about modification of the entrance to the nuc itself?
What's involved in fitting one of those disc entrance closing/guarding thingies?
What is the easiest way of overcoming the awkwardness of the the original entrance being recessed?