I have a couple thermos bottles (double wall stainless) that are too small of a diameter to fit snugly in a conventional water bottle cage. i cut some inner tube rubber strips and wrapped around the bottles several times to give me the necessary outside diameter to match the cage capacity, then wrapped plastic electrical tape around the rubber strips to hold the rubber wrapping in place.
I do not have any good photos, but I plan to do an exercise bike ride later today on my foldup bike, if I do that I will try to snap a few photos to post.
In other words, instead of adjusting the cage to fit the coffee container, I adjusted the coffee container to fit the cage. And this way I can use the thermos in any of my bikes.
Last week one day it was about 3 to 5 degrees C in the morning and about 20 degrees C in the afternoon. I brought one thermos of hot coffee for morning, one thermos of iced coffee in afternoon. It was perfect planning for a long bike ride that was interrupted half way through by a good lunch.