o2 sensors and custom exhaust

[boxerpower]

hey guy can any one tell me which o2 sensor controls the fuel mix, and which one just checks the cat. because im planning to have a 90* elbow fabbed off the headers to a aftermarket/universal cat and then have the rest of the pipping go to a can exhaust. [i get the cel code po420 (cat deficiency)] so im hoping the fix will also get rid of my cel codes. but im just going to have one bung put in the pipping which ever one controls the fuel and leave the rest of the o2 sensors plugged in but tied up, up underneath the car. im in california and have to have a cat. does any one see any flaws in my plan/idea?

[rougeben83]

front is afr, rear is check.