Well, if your cat is like mine, you might have an ongoing battle on your hands! Here’s something you can try, though… vegetable shortening. You can try putting it (generously) on the branches that your cat uses to get into the bush. Believe me, he will not like the shortening on his paws, but it will be harmless to him even if he eats it.
It should even be harmless to apply directly to your butterfly bush’s bark, but you might want to try a little area for a week or so to see if there are any adverse effects. If you see something you don’t like, then maybe try wrapping the cat-perch branches in plastic and put the vegetable shortening on the plastic instead of directly on the bark.
I’ve used this same technique to keep squirrels from climbing up the pole that supports my bird feeder… they still make it sometimes but is it ever funny to watch them try. 🙂
Hope that helps!