I had a local tuner log into the ecu, edit the map and permanently remove the DTC P0420 code. For my 07 that is the only real option.
For your year, I'm not 100% if the others will work but took the guy 10 minutes and never had a problem again.
Wrapping your headers will not 100% solve the problem but will take away the sewing machine sound cause by the thin walled headers.