I am not an expert but you might be able to drill a hole and weld a nut to the hole of proper size in order to connect your second O2 sensor. Sometime this works, sometimes it does not. I had a similar situation in which I replaced my cat with a test pipe and tried putting the O2 sensor in the test pipe. ODBII does not like that very much. Needless to say I had to put my cat back on and sold it to my cousin that has an ODBI Accord. It worked for him since he does not have a sensor at the cat.