I can only imagine that she would spend more time pulling her Zhu Zhu Pets around in a box than anything else if she had something like the Rolobox that puts wheels and a pull string on the box. Honestly, I would have played with something like this more than anything else when I was a kid too.
It appears that the stuff sticks to the cardboard box with simple pushpins. I would bet there is something on the inside of the box that will hold the parts on or they would fall off constantly. Your kids should be able to use this set up with boxes of all sizes. You can order the kit up right now for $14.