[elwesso]

Has anyone tried those little gizmos that trick the o2 sensors? I have heard of other cars (mustangs come to mind) that use something that plugs into the harness for the o2 sensors...

As long as the cats are there, you should have no issues passing emissions, so really all you're trying to is prevent the CEL so that you can pass emissions.

I read some people on the M3 forums that had varying degrees of success using those "o2 sensor trickery devices".. Some people claimed they worked, others claimed they didnt... I know they can be obtained pretty cheaply, so perhaps it'd be worth trying before having the exhaust modified.