I've had good luck with Grab On Grip covers. I like the extra thickness and they help my hands from cramping. They run about $12.00. I know the heavy bar ends would help also, but they are quite a bit more expensive.
The bike also smooths out a bit as the engine breaks in. The fuel economy goes up a bit too...
You could try some softer grips, and see if that helps. Stock grips, seemingly regardless of make and model, seem to be of the hardest rubber they could find. If that's not enough, then HVMP bar ends that landman mentioned are the way to go. I had them on a FZ6, and the difference was huge. My N1K already had them on it, and the vibes are minimal. Lets just say, those bar ends will never come off the bike, lol.
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