You can decat the car and install a MIL eliminator by Farley (3979650).
Got his name a while back, I talked to him last year so he replaces the cat with a pipe.
I never did because the CEL cleared by itself and from reading on the net it seems to be a common problem with these cars.
Change back to premium and run the car for a week it usually goes away for itself.
Changing the oxygen sensors will not help if the readings are within parameters the CEL will come back.
Changing the cat with a good foreign used one (hard to tell) should prevent it from reoccurring.