I think this is probably a very good idea!
Put a ferret in your attic and seal it up. I'm sure you won't have a mice/rat problem anymore. I mean, at the very most, you're out one ferret. And who can get too attached to something that smells like a gerbil...
I say don't feed him so he's hungry and if you still have a rat problem after 2 weeks add a cat named Schrödinger and never look in there again.
Let me know how it goes beceause I just told my girlfriend she should get rid of the squirrels in her attic the same way....
Bredbeddle