Exhaust fan grille extension?

When you're an amateur it's often the simple things that stump you. I've installed a cedar ceiling in my bathroom -- I did a nice job and it looks great. The cedar is 5/16ths and I used a 1/4 inch strapping, so I'm 9/16ths lower than the old original drywall ceiling. The final step in this project is to re-install the exhaust fan grille but the darned wire spring-clip thingies are too darned short. The grille won't go in far enough to allow the spring action to pull it up; instead it gets pushed out and refuses to do anything but hang about a half-inch below the ceiling. Grr! This second-floor bathroom was newly-constructed a few years ago and the contractor did a great job of sealing everything very nicely -- I'm not thrilled about moving the fan down a half-inch or so. How does one deal with something like this, short of installing the grille to the ceiling with screws or something drastic like that. Thanks very much for the help.