ORIGINAL: da Rock
You can also use an exhaust diverter on it. They are extensions that put the exhaust into the airstream a bit farther away from the airplane.
Sometimes where you point the exhaust works wonders. And sometimes just a bit further out is enough.
I agree with Rock. I have used diverters for exactly what you want to correct. They are inexpensive, very light and don't add weight and can be set up without altering your existing muffler.