I love the smell of cigarettes on ponies, reminds me of my grandparents
But that cat-litter idea really sounds great!
But I thought then, you probably should get that white see-through crystals kittylitter. And you can put the whole pony in it. Normal kitty litter gives so much dust, and has also a odor.
Here we have these little bags that smell like fabric softener, to hang between your clothes, so they smell nice. Put them in a bag with that?
Grandma says:
Cleaning acid. Don't know the English word. It is like vinegar, but with something in it that makes it non-edible. Don't know the effect of direct contact on the pony-plastic though. And it will smell sour afterwards. What you can do is lock the pony up with a sponge with the acid, to avoid direct contact.
Charcoal. Lock the pony in with some charcoal (no touching, like the acid/vinegar)
Good luck!