Hello there,
Have you tried bitter apple spray or paste?  I bought some at both
Petsmart and the Ferret Store on-line.  It's supposed to be safe and
tastes horrible, though one of my ferts likes the way it tastes, he's
kinda a strange ferret anyway.
 
Also maybe some Chew Weasels, N-Bones or Foamy Fries would distract them
and satisfy the desire to chew.
 
Best of Luck to you.
Take care,
Suzi and da ferts- Cheechie, Chongie, Goose, Mookie and Ruby
[Posted in FML issue 3686]