Who says cats don't have grabbing appendages? Ever tried to deal with a frightened cat who wanted to put you between them and whatever they were scared of? Like if Velcro were made out of fish hooks - they can grab like a hot damn, and in my experience "damn" is the very least of what you'll say when they do.
More to the point, cats climb trees with their claws, so making ISS interior surfaces amenable to feline use is just a matter of finding a material that's enough like bark for them to get a grab, and durable enough to hold up under long use.
