For what it worth, I've used a home-made remedy with great success on the 2002 HD 883R rigid-mount Sportster (a "paint shaker") that tugs our little sidecar rig: Remove grips, insert clear silicone type caulking into the handle bar ends, insert a roll (1-1/2 for me) of plastic-wrapped pennies slathered in the silicone caulking, plug the end with more clear silicone caulking, let the end cure, re-install grips (I did gel-type grips). Apparently, the pennies, being slightly smaller than the inside diameter of the handle bar, kinda float around in the caulking for a similar result. Smaller diameter bars would require something smaller than pennies.
I've been very pleased with the result. Vibration in the grips has been noticeably reduced, such that I can ride most all day without my hands going numb. If you already have the clear silicone caulking, cost is about $2 - plus new grips. And I'm glad it worked, as I don't have a clue how to clean it up.
By the way, this is not my original idea; I merely followed a suggestion found on xlforum.net. Lee