Folks have mentioned here that chest carry could work, how about a J-frame 642 in a belly band where the weapon is adjacent to the stomach. Thinking out loud, I would think bone falling on a weapon would do more body damage than having the weapon adjacent to my relatively soft stomach and hitting the deck (natural body curve and all). But honestly I don't know what is best. I have a Harley Ultra (touring) and they don't lend themselves to tank carry at all. I don't see myself ridng and shooting (I wear gloves, full helmet and armored jackets) and it would be awkward to be moving the handgun back and forth between me and the scooter when I am eating or gassing.
I would like to see discussed in what forms would a biker likely confront a threat or have encountered threats. While on the bike in motion or at a stop light or off the bike? I feel very vulnerable while touring and biking. Any thoughts? It is a challenge.