Why not thread a few of your ratties fave treats and hang them up in the cage for them to nibble at!
I tried peapods and cut up carrot chunks , not only did it look colourful , it was a healthy snack too and it beats them chewing other things in the cage My girls enjoyed nibbling, pulling and hiding bits they pulled of the string.
It's a great Boredom Breaker!
Sayj