You may also want to consider the Bar Ender helmet locks. They are basically bar end weights that are secured with a key.
It may work, IF:
You are using helmets with standar D-Rings
You do not have hand guards, or don't care about them
I have been told the hand guard mounts interfere with the bar enders, but I don't have the hand guards so I can't say..
You should be able to find them at
www.barender.com
My friend has them installed on an older Suzuki. He loves them.