Damn i was gonna tell you cheat....e85 mix about 30 % in always would pass sniffer without cats in PA. Also idle timing can effect he readings a smidge.
That was my trick as well for a 1990 Ford Rapevan I had. It failed the sniffer, took it to the gas station to get 30% or so of E85, ran the balls off of it to keep it hot just before pulling up and went straight to the sniffer. Passed with no other modifications