Jon,
There used to be a product called the handlebar snake. It was weighted rubber or sumpin' and you slid it into your bars and it dampened the vibration. Never used one but I heard they worked.
Also, you will find a sweet spot in the RPM range where the motor sounds great and the vibration minimal. That's when the engine is "on" and all is good. In top gear mine is at 58-60 mph indicated (with 18T cog).
-Jesse, who's "Ennie" gets better every day!