My ferret rolls around in her litter box. How can I deter her from doing this?

She will only roll around in a retalively clean litter box, so usually when I clean their cage I'll leave a little waste so she recognizes it as a toilet and not a play thing, but she continues to roll around in it. I've given her a big box of rice to give her something she is allowed to roll in, but she still prefers her litter box. When I see her playing in her litter box, I will pick her up and place her in the rice instead but this doesn't seem to help. For my litter I use yesterday's news recycled paper pellets, what are other products I can use for litter?