Yep!
We tried white mouse, cream-colored ASF rat and black-colored ASF rat of different sizes hopper and smaller, and a rat pup, in the RUB, in a deli cup, in a completely dark cardboard shoebox. No dice.
No, we didn't try braining. None of us were willing to do it.
He assist-fed again today. At least it is easier now - he doesn't try to spit the rat out anymore.