You probably know that some bikes have weights in the ends of the handlebars to cut down on the vibration. They are pretty much just pieces of pot metal with rubber dampers insulating the weight from the inside of the handlebar. I'm thinking you could easily pick some up or maybe rig something up.
I had them on one of my bikes and removed them and the bike still feels great. My other bike never came with them and my body feels like its ringing like a bell every step I take after being on the bike for 2 hours. Who knows if they are helpful?