put my stock cats back on for the smog test. Although judging by the NO numbers I threw at my smog test today, either my old cats are just about shot or I've got EGR problems. But he got it to pass on the 2nd run, fortunately. But I'm in agreement with you that adding some plumbing to the Specialty Z hi-flow cats would be much easier.
Maybe a muffler shop can work something up for you. I was looking at my stock cats yesterday, and it looks like pretty standard plumbing hardware. I guess the only concern would be breaking up the airflow in the pipe.