I don't know if it is possible to shift right back in cat form after you cast FF with the silence glyph, but for the moment I'm using this:
/cast [@focus,exists,harm,nodead] Growl
/cast [@focus,exists,harm,nodead] Faerie Fire;[] Faerie Fire
Edit: Growling in a form, different than bear, will turn you into that [bear] form with no global CD.
If you have a focus target - let's say a healer - pressing it will instantly turn you in bear form and cast FF, with no GCD lost
If you don't have a focus target, you will cast it on your current target.
This will not work in 5.2 because of the Growl change though :|