You can add paper. If you put whole sheets under the regular bedding they have a ball pulling it up and shreding it. It's better than a wheel!

I use my local weekly paper, it's free and made with soy inks, totally non-toxic.

The downside is the paper does not mask the smell so it can get bad. Since I rotate my male around and in my opinion he's the only one who outright stinks I just don't paper the tub he's in.