It's a nice idea, but you'd probably be better off getting HFC's or TP's.
I guess if you can get to them easily enough, and can do the work yourself, no harm in experimenting, but those cats are a real pain to break loose -- search for "demon bolts"...
EDIT: Actually, come to think of it, are you sure that's not just a resonator you're referring to -- I've seen several sets of cats off the car, and I didn't think there was more cat after the O2 bung
