Aashley -- that's the type I wanted! They only had small like those for the bobbins. I think the large ones can be twisted on to the less-than-half cones better than the regular elastics, which are great at full but won't get smaller easily.
But thanks all for the ideas! I plan on going to the Goodwill today to look at those bamboo cutlery trays -- I think one would be perfect for the Aurifil.
Don't think I'm going to be able to find those notches reliably/easily. Since I bought the elastics, for now maybe I'll try some that way and some with blue tape to do a comparison. I like the idea of simply taping it to the base, don't know why I didn't just stop there instead of mentally putting it inside.
Yesterday at my Tuesday group I was given a stash clearing UFO that is just gorgeous and I once again, I got distracted by fabric (sing to the tune of Blinded by Science0.